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Author Topic: 110 Electrical Guru needed  (Read 4868 times)
bobofthenorth
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« on: June 02, 2009, 04:19:09 PM »

The picture is of my transfer switch.  One of the joys of owning a bus that somebody else converted is that you get to play Sherlock Holmes fairly often.  Today the topic is: "How does my transfer switch work?"  The first step in answering that question for me anyway is to figure out what I have.  Can somebody please identify this beast?  I can't see a name on it and it is in an aluminum housing that Bruce Coach obviously fabricated with a BC certification sticker stuck on the outside of it and no other markings.



My goal is to delay the switch-over from inverter to generator in some easy fashion.  My Kubota rebuilder went on ad nauseum about how I shouldn't start the Kubota and immediately put it to work.  He's probably right and it seems to me that there is likely some simple way to accomplish that with the existing x-fer switch but first I need to figure out what I have. 
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« Reply #1 on: June 02, 2009, 05:09:53 PM »

Bob,

I can't identify make or model from what you've shown.  Many switches look just like this one.

I can tell, you, however, that I see several problems with it right off the bat.

Chief among those is the fact that the neutrals are all tied together.  Assuming there is a ground-to-neutral bond in the generator, this will give you a multiply-bonded system whenever you connect to shore power, a potential hazard.

There are also several color-code problems, at least one bare wire that should not be, and some shoddy workmanship in general.

The little circuit board on the top of the picture controls when the switch transfers from shore (which appears to be default here) to genny.  It does not look to be of an adjustable-delay type, but you can add a simple delay timer in the sense lead running from the black genny terminal to the circuit board.

If it were my coach, I would replace the switch with one that switches all three current-carrying conductors and has an adjustable delay timer built in.

Give me a call if you want to discuss in further detail.  My phone number is on the "Who We Are" page linked off the blog (in the sidebar on the right).  Not posting it here so it does not get harvested by bbs-crawlers.

-Sean
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« Reply #2 on: June 02, 2009, 07:27:03 PM »

Sean I just checked this with a DVM and you are correct that the genset has the neutrals bonded all the time. You are right -- a 3 conductor xfer switch would alleviate this problem. The neutral bus and the ground bus are completely separate in this panel.  Any reccs for a mfr of a 3 pole switch?  Preferably one that will be available on the eh side of the 49th parallel.

As far as the delay after the genset starts you have already told me enough to accomplish what I need to.  I'm going to put a simple toggle switch in what you called the "sense lead" so that I can control when the circuit board sees power from the genset.  

FWIW the colour code issues you refer to are actually dealt with through tape wrapping.  There could likely be more tape wrapping but there is enough that it is clear what the wires are when you can see the panel.  I gather there is some code issue with the bare wires?  
« Last Edit: June 02, 2009, 07:34:08 PM by bobofthenorth » Logged

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« Reply #3 on: June 02, 2009, 09:33:02 PM »

...  Any reccs for a mfr of a 3 pole switch?  Preferably one that will be available on the eh side of the 49th parallel.


The canonical "standard" for the RV universe seems to be the IOTA:
http://www.iotaengineering.com/its50r.htm

This unit is available from many retailers on-line and brick-and-mortar, and is listed in both US and Canada.  About $160 or so.  Personally, however, I don't favor it, because of the way the switching is implemented internally.  I favor the model 501 from Parallax Power:
http://www.parallaxpower.com/ATS.htm

I found this predecessor to the 501 on-line, looks like they will ship up north:
http://www.dan-marc.com/1-ats5070.html

And this looks like it would work fine and be shipped to you as well:
http://www.rvpartscenter.com/ProductDetail.asp?ProductID=20497&StoreID=14&DepartmentID=65&CategoryID

All of the above switch both hots and the neutral, and have built-in generator delay timers.

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FWIW the colour code issues you refer to are actually dealt with through tape wrapping.  There could likely be more tape wrapping but there is enough that it is clear what the wires are when you can see the panel.


Well, I have to confess that I don't really know what the code says on, how did you put it, the "eh" side of the 49th.  But down here, tape wrapping is never allowed on a ground wire -- that needs to be either bare copper or green, with optional yellow stripe, for its entire length.  You can't simply put green tape on the end of a red wire.

Also, all conductors must be properly identified and the method of identification needs to be clear.  On your installation, the input conductors from the shore and genny appear properly identified, but after the relay, both hots are red all the way out -- no way to tell the two hots apart.

Looks to me like they got a fire-sale on red wire.  I have to say, if this is the level of work coming out of Salmon Arm, my opinion of Bruce has dropped a few notches.

Quote
I gather there is some code issue with the bare wires?  


The bare ground wires are fine.  I thought I saw a bit of bare wire on one of the hots coming from the genny, but that could just be the way the photo came across.

Also, FYI, some of the wires look to be too small for the application.  Notably, the genny lead-in, although I don't know what size unit you have.

HTH,

-Sean
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« Last Edit: June 02, 2009, 09:36:01 PM by Sean » Logged

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« Reply #4 on: June 03, 2009, 04:07:00 AM »

All of the above switch both hots and the neutral, and have built-in generator delay timers.
Thank you sir - we will be in Calgary next week where I expect I will be able to find what I need now that I have a half-assed idea what that is.

Quote
Looks to me like they got a fire-sale on red wire.  I have to say, if this is the level of work coming out of Salmon Arm, my opinion of Bruce has dropped a few notches.
Be gentle with Bruce.  This coach is serial number 1 or damn close to it.  More importantly the P.O. (AKA Doofus) had some kind of dust up with Bruce toward the end of the project and ended up taking the coach home to "finish" himself.  Any time there is an electrical issue I can usually trace it to Doofus's work although I believe that this panel was part of Bruce's work. And FWIW the panel does have a BC electrical inspection sticker on it which means that somebody with a clipboard and a blue suburban was at least close enough to it to put the sticker on.

Quote
 
Also, FYI, some of the wires look to be too small for the application.  Notably, the genny lead-in, although I don't know what size unit you have.
You are right, they do look marginal.  I will check that out against my favorite online gauge calculator because I am virtually certain that doofus installed the gennie.  It is a 6500 watt 240 volt unit FWIW.
« Last Edit: June 03, 2009, 04:16:22 AM by bobofthenorth » Logged

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« Reply #5 on: June 03, 2009, 05:34:22 AM »

What is the color code standard for wiring in an RV?  I would think that the standard house AC wiring color codes would be followed for RV wiring - bare/green ground, white neutral, black hot, red alt. hot.  The only tape wrapping that I am aware of being allowed is to wrap white for black when you are using /2 romex to wire a two station light switch.  But what is the standard for DC wiring?  I confess I like to use red for hot and black for ground, but that raises the issue of confusing 12vdc black gnd for 120vac black hot, which i don't like at all.  I'm just getting ready to redo all of my DC wiring.

I just ordered  an IOTA transfer switch for the power upgrade I am doing on my bus.  I'm setting everything up for 30 amp 120vac service.  My gas generator has switches to disable power output while starting.  It is a 6600 watt gennie, with two 30 amp output sections, so I will run the bus off one side (the 120/240 side) and save the other side for off-bus uses.

Brian
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« Reply #6 on: June 03, 2009, 05:56:14 AM »

There is a CSA standard for RVs. Here is one source.  I expect you can get it directly from CSA as well but I didn't take the time to look.

There is also a Canadian Electrical Code (CEC) which is similar but not identical to NEC.
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« Reply #7 on: June 03, 2009, 06:39:34 AM »

I agree with Sean on the difference between the Iota type transfer and the Parallax type.  The former uses two DPDT contactors, one for the power leads and one for the neutral.  It is possible for one to fail leaving the neutral untransferred.
The other type (Todd Engineering/Lyght Power Systems/ESCO) use two three pole single throw mechanically interlocked contactors.  These are inherently fail safe. They require either shore power or generator power to operate. Without either source, there is no connection at all.

The latter are actually made from a three phase motor reversing contactor with an auxiliary contact and time delay circuit. Those knowledgeable in motor controllers could probably fabricate their own at considerable savings. They are more expensive that the Iota type but safer and more robust in my opinion.
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« Reply #8 on: June 03, 2009, 06:56:12 AM »

The latter are actually made from a three phase motor reversing contactor with an auxiliary contact and time delay circuit. Those knowledgeable in motor controllers could probably fabricate their own at considerable savings. They are more expensive that the Iota type but safer and more robust in my opinion.

Keep going with that thought please.  I'm happy with the control circuitry, all I'd like to do is swap out the current 2 pole contactor for a 3 pole contactor. 
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« Reply #9 on: June 03, 2009, 08:47:08 AM »

Be gentle with Bruce.  This coach is serial number 1 or damn close to it.


Oh, OK.

Quote
You are right, they do look marginal.  I will check that out against my favorite online gauge calculator because I am virtually certain that doofus installed the gennie.  It is a 6500 watt 240 volt unit FWIW.


OK.  A 6,500 watt genny will produce a tad less than 30 amps at 240 volts -- I would wire that with #10.  All the 50-amp stuff should be wired with #6.  Hard to tell from the photo what gauges you actually have in there.

What is the color code standard for wiring in an RV?  I would think that the standard house AC wiring color codes would be followed for RV wiring - bare/green ground, white neutral, black hot, red alt. hot.  The only tape wrapping that I am aware of being allowed is to wrap white for black when you are using /2 romex to wire a two station light switch.


The identification standards for 120/240VAC wiring are the same in RVs as in other types of uses.  The code does allow for field identification of conductors using a durable marking system such as colored tape at the ends.  The identification must be done at each panel, fixture, junction, splice, etc. and it must be consistent.  Ground wires are not permitted to be identified in this manner (until you get into very large gauges), they must be bare, green, or green with yellow stripe for the full length.


Quote
But what is the standard for DC wiring?  I confess I like to use red for hot and black for ground, but that raises the issue of confusing 12vdc black gnd for 120vac black hot, which i don't like at all.


There is no code standard for wiring below 30 volts.  I recommend you follow whatever system your coach manufacturer used to identify hot an ground.  There should be no opportunity for confusion with the AC wires because those are required to be separately enclosed.

Quote
...  I'm setting everything up for 30 amp 120vac service.  ... I will run the bus off one side (the 120/240 side) and save the other side for off-bus uses.


I'm not sure I follow this -- why set the coach up for 120 only if you have a 240 genny?  Also note that if you have more than five circuits or two thermostatically controlled appliances (e.g. an air conditioner and a water heater), you are required to install a 50-amp, 240-volt system.

I agree with Sean on the difference between the Iota type transfer and the Parallax type.  The former uses two DPDT contactors, one for the power leads and one for the neutral.  It is possible for one to fail leaving the neutral untransferred.
The other type (Todd Engineering/Lyght Power Systems/ESCO) use two three pole single throw mechanically interlocked contactors.  These are inherently fail safe. They require either shore power or generator power to operate. Without either source, there is no connection at all.


Yes, this is precisely what I meant when I said I did not care for how they were wired internally.  I was just trying to keep the discussion simple...

Quote
The latter are actually made from a three phase motor reversing contactor with an auxiliary contact and time delay circuit. Those knowledgeable in motor controllers could probably fabricate their own at considerable savings. They are more expensive that the Iota type but safer and more robust in my opinion.


If you go to the electrical section on my web site, you will see that we did exactly this (http://ourodyssey.us/bus-e-ats.html).  I used a Telemecanique reversing motor starter as the core, and added other components to achieve the delay and some other things I was trying to do.  Also, my genny puts out 70 amps, so the 50-amp factory units were not big enough for us.

Keep going with that thought please.  I'm happy with the control circuitry, all I'd like to do is swap out the current 2 pole contactor for a 3 pole contactor.  


Bob, I found my contactor on eBay for perhaps $50 (the size I used probably runs ten times that much at retail).  What you are looking for is a "three phase reversing motor starter" rated for 50 amps (although contactor ratings are somewhat bewildering).  You can buy them retail from places like Grainger, but they are pricey.  If you find one, I can help you get it hooked up.  The IEC type is generally smaller for a given rating than the NEMA type, which may be a factor if you intend to use the existing enclosure -- I used an IEC model.  You want a NEMA size 3, or an IEC model with a rating of 50 amps "AC-1."

This is what you will find inside the units I suggested, with the added advantage that there will also be the delay timer circuitry included, something you will need to add if you just swap contactors.  Delay timers are also fairly spendy.  These can be had from Grainger, Allied, Newark, etc..

-Sean
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« Reply #10 on: June 03, 2009, 11:29:04 AM »

Sean,

The breadth of your knowledge is impressive.  Your interest and research into the proper method of accomplishing a project, whatever it may be, is a value I share.

Your communication skills and attention to detail however, are in a different league from most of us mortals Smiley

Thank you so much for sharing, you are appreciated.

Len
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« Reply #11 on: June 03, 2009, 12:31:44 PM »

Thanks, Len.  Always good to feel appreciated, especially after taking so much flak for being the safety Nazi.

-Sean
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« Reply #12 on: June 03, 2009, 12:49:56 PM »

For the time delay, you could probably use an air conditioner compressor delay unit, some can be adjusted from 10 sec to 10 minutes and run $30-$50.  Nick might be able to help on that front.
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« Reply #13 on: June 03, 2009, 01:03:13 PM »


 Sean,

    I'm surprised you made reference to a political party  Shocked

   I'd be more afraid of a self reference to SS though.

   Are you taking any pictures if how the leaks are being fixed on your bus?

   Just interested on the hows and maybe you'll start a thread on it.

 Skip
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« Reply #14 on: June 03, 2009, 01:08:17 PM »

The circuitry I have already has a delay built in.  I have never timed it but its likely 15 or 20 seconds.  Long enough that I can walk around the bus and hear the transfer switch click in.  My intent is to manually delay the existing delay so that I can control the warm up time for the Kubota.

And ............. what Len said.   Wink
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« Reply #15 on: June 03, 2009, 01:18:33 PM »

The circuitry I have already has a delay built in.  I have never timed it but its likely 15 or 20 seconds.  Long enough that I can walk around the bus and hear the transfer switch click in.  My intent is to manually delay the existing delay so that I can control the warm up time for the Kubota.


OK, but if you intend to use the existing delay circuit and just change from the existing DPDT relay to a three-pole contactor, you will need to first find out what voltage the delay circuit puts out.

While it might be common sense to think it is 120VAC, it is actually fairly common that the control signal ends up being DC (due to the way the delay electronics work).  So the coil on your existing relay might be 110VDC, rather than 120VAC.  It ought to be marked on the relay itself, but, if not, get your voltmeter out and measure at the coil terminals.

If you do have a 110VDC coil, that will complicate the contactor installation.  You will either need to change one of the contactor coils, so that one is 120VAC and the other 110VDC, or you will have to rectify the shore power sense lead to 110VDC and get a contactor with two 110VDC coils.

Did that make sense?

-Sean
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« Reply #16 on: June 03, 2009, 01:29:06 PM »

Sorry, one further note, about "priority":

The switch you have now could be considered to be "generator priority," which is to say that, even if shore is connected and hot, when the generator comes on-line, the switch will transfer the load to the generator, and the shore will be idle.

With an interlocking contactor, the priority is FCFS -- if both sources are hot, the load will be connected to whichever source was hot first.  So if shore is hot and connected, merely starting the generator will not cause the load to transfer.

This can be fixed by running the shore sense lead through another NC relay, energized by the generator, so the shore contactor will be interupted on genny start-up.

One way to accomplish this cheaply, which would also solve any incompatible voltage issues with the existing delay circuit, is to use the existing DPDT transfer relay as a "control" relay.  One pole, operating in the NC mode, would be used to interrupt the shore sense, to open the shore contactor, and the other pole would be used in the NO mode to provide standard 120VAC operating current to the generator contactor.  The downside, of course, is now you have to find room not only for the three-phase motor starter (which is, itself, much larger than what you already have), but also for the existing relay.  Probably a tight fit in your existing enclosure.

This might be another factor which drives you to just change out the whole unit for one that already does what you want.  FWIW.

-Sean
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« Reply #17 on: June 03, 2009, 01:59:27 PM »

OK - I got in there with a magnifying glass looking for a voltage on the coil and discovered a part number on the switch or maybe 'relay' is the right word.  It is a Deltrol Controls 900Q DPDT 20791-84.  110VDC coil, 1.5HP or 30 amp @ 120/240 contacts. 

Before this project gets runaway complicated, wouldn't this relay work off my existing delay circuitry?  I'm quite prepared to manage the generator and I don't think I want it to be starting up on its own.  The goal of this project is only to remove the generator neutral bond while I'm on shore power.
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« Reply #18 on: June 03, 2009, 02:07:43 PM »

Bob,

If you have a 50-amp shore setup, the relay you linked is too small -- contacts rated only at 30 amps.

Of course, it seems the one you have in there now is also only rated at 30 amps.  Which itself is a problem if you have a 50-amp system.

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« Reply #19 on: June 03, 2009, 02:10:13 PM »

Bob,
If you are careful managing your power use, that is not turning on any major loads until the generator is up to speed, you can get away without the delay.  The air conditioner(s) probably have their own built in delay.  You still need a relay or auxiliary contact (available on most reversing contactors) to establish generator priority.
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« Reply #20 on: June 03, 2009, 02:14:07 PM »

Hey, look what I found.  Once you posted the part number for the relay, I found the manual for your transfer switch:
www.escousa.net/Merchant2/graphics/00000001/LPT30TrblShootRepair020206.pdf

Looks to be an ESCO model LPT30, which is a 30-amp, 120-volt (only) RV transfer switch.  So in addition to poor wiring practices, looks like they also forced a 120-volt ATS into a 120/240-volt application (which is why you now have the neutral problem), and too small to boot.

Again, if you have a 50-amp, 120/240 system, I recommend you replace this with an ATS of the proper rating.

The more I think about this, the more I wonder if Bruce didn't wire the coach properly, and then "Doofus" modified this switch when he put the genny in?

-Sean
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« Reply #21 on: June 03, 2009, 02:17:52 PM »

...  You still need a relay or auxiliary contact (available on most reversing contactors) to establish generator priority.


Len,  the aux. contacts on the reversing starter itself, while sufficient to keep things safe by not allowing the opposite contactor to energize, will not by themselves allow you to establish priority.  Once the shore contactor is energized, there is no way for the generator contactor to open its NC aux. contacts (and vice-versa).  You absolutely need another relay.

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« Reply #22 on: June 04, 2009, 08:12:17 AM »

Well Sean, it looks like the commercially available units are actually "Shore power priority".  This is what I have in my MH,  a Todd Engineering PS-250.  The Lyght and ESCO units are identical.

http://www.generatorjoe.net/html/esco/LPT50CA.pdf
http://www.escousa.net/Merchant2/graphics/00000001/LPT50CATrblShootRepair091906.pdf

The ESCO LPT50CA mentions a "Shoreline Release Switch, 120 VAC, N.C." which I guess is to force it to switch to generator even when shore power is available.

Len
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« Reply #23 on: June 04, 2009, 08:25:52 AM »

.. a "Shoreline Release Switch, 120 VAC, N.C." which I guess is to force it to switch to generator even when shore power is available.


Right...  that would simply interrupt the coil voltage on the shore contactor long enough for the genny contactor to close.  To implement generator priority, I would propose a 120VAC, NC relay to do the same thing, energized from the generator.

I have a similar setup, only, in my case, I used an extra set of contacts on the generator delay timer.  When the timer expires, operating voltage to the shore contactor is interrupted, and operating voltage to the generator contactor is supplied.

-Sean
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« Reply #24 on: June 04, 2009, 03:15:46 PM »

Hey, look what I found.  Once you posted the part number for the relay, I found the manual for your transfer switch:
www.escousa.net/Merchant2/graphics/00000001/LPT30TrblShootRepair020206.pdf
Looks to be an ESCO model LPT30, which is a 30-amp, 120-volt (only) RV transfer switch.  So in addition to poor wiring practices, looks like they also forced a 120-volt ATS into a 120/240-volt application (which is why you now have the neutral problem), and too small to boot.

I agree that schematic looks remarkable similar to what I have but my relay has 120/240 stamped on the side of it right next to the UL/CSA stamp so its definitely a 240 volt relay.

Today I found a Parallax 5070 ATS at one of the RV dealers in Saskatoon.  It was pricey but it would have been pricey to import one too - probably not much difference by the time it got here.  The one I have switches all three poles, has a microswitch on the neutral contactor and has a built in delay which I think I can defeat in order to take control of how long the genset runs before I put a load on it.  I'll need to get another spool of red wire in order to complete the install.   Grin  This unit also has a set of auxiliary contacts - one NO and one NC - but I think I'd need an engineering degree to figure out what to do with them.   Shocked  Thank you guys for all your help - maybe I'll get around to posting some pix of the completed install - but maybe I won't if I find that spool of red wire.

We ended up tearing the ATS apart on the parts counter because I actually found a service manager who was more interested in learning than pretending he had all the answers.  The documentation with the switch is pretty sketchy and we couldn't tell whether it switched the neutral so we tore it apart to see.  I kept apologizing for being a PITA and he kept saying "no - we need to know this too."  I like that attitude.
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« Reply #25 on: June 04, 2009, 04:25:19 PM »

I agree that schematic looks remarkable similar to what I have but my relay has 120/240 stamped on the side of it right next to the UL/CSA stamp so its definitely a 240 volt relay.


Bob, that's just the rating of the individual relay itself -- almost all such relays are rated for both 120 and 240.  It does not reflect the rating of the transfer switch assembly as a whole.

Since Esco has always made quality stuff that properly switches the neutral, I conclude that what you have is, indeed, the LPT30 (which, as I already mentioned, is a 120-volt assembly but contains exactly the 120/240 relay you have), and it has been subsequently mis-wired to switch two hots instead of one hot and one neutral.  That accounts for your neutral problem, as well as the mismatched screws on the terminal strip.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #26 on: June 04, 2009, 05:54:08 PM »

OK - I didn't understand what you were saying but that makes sense.  I think we gotta blame that one on Bruce BTW and now I'm not sure who to blame for the shore cord that we used to have.  Up until we let some smoke out last spring we had this great big professional looking SS Marineco 50 amp connector and a shore cord the size of an adult python.  The Marineco had leads running into a junction box and then from there the hard line ran to the panel.  Last spring a screw must have loosened up in the junction box and eventually the smoke got out.  When I started digging into matters to figure out where the smoke was missing I eventually discovered that my shore cord (remember - its the size of a python and it has 50 amp connectors on both ends of it) was only a 3 conductor cord.  No problem there, is there? 

There were a variety of locations where the two hots were tied together including the aforementioned junction box, the panel that I have already posted a picture of and the main panel.  Up until now I had blamed all that on doofus and I'm still not sure who was responsible for that but this x-fer switch I think falls on Bruce.  We're not big power users obviously because I had never figured out that we only had one leg.  I think we had only ever been on 50 amp service maybe two times so we hadn't really ever tested it I guess.
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« Reply #27 on: June 05, 2009, 06:27:40 AM »

Bob,

I'd like to return to the beginning of this conversation and question the need for warming up the generator for any length of time before loading it.

A little load management should take care of it.

I think 30 seconds is plenty of time for the transfer switch to operate as long as you are not slamming a 40-50 amp load on the genny.  In addition, the air conditioners will have another 30 seconds or so before the compressor kicks in.

The big loads should always be turned off before connecting either to shore power or the genny and then turned on manually after connection. 

A small (10-12 amp) load as soon as you have oil pressure and full speed will not hurt the engine.

If you are operating in sub-freezing temperatures, a moderate load will help it to warm up quicker.

Len
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« Reply #28 on: June 05, 2009, 06:48:07 AM »

That is really good counsel Len and if it wasn't that my mechanic is the Super Uke I would thoroughly agree with you.  There was some minute evidence of damage on my pistons when he tore the engine down.  I don't suppose anybody else would have noticed or worried about whatever he found but after he got done yelling at me about how dirty the engine that I had just pressure washed was he started in on my bad operating procedures.  This man has actually been thrown out of curling rinks for bad behaviour (apparently you can't throw your broom at a team mate who misses his shot - who'd a thunk?) but he is an exceptional mechanic.  He'll probably never know what I do but on the off chance that he may find out I want to do it "right". 
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« Reply #29 on: June 05, 2009, 07:09:17 AM »

Someone please educate me on the need to let the genset warm up before applying a load.

Again, I come from the boating world and it is normal practice to start the genset and hit it with everthing at once.

I understand that in a perfect world, warming the genset will increase the life span of the diesel but in the real world, does it really change much?

On the other end of the scale, allowing the genset to cool for a few minutes once the loads are transferred makes a significant difference in the longevity of the genset.

I am just trying to understand why this is so different than what I am used to.
 
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« Reply #30 on: June 05, 2009, 07:20:36 AM »


 Darn and here I thought checking was allowed. Was he called for high brooming?

  Warm up warm downs whoa no wonder my gens don't last....

 Skip
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« Reply #31 on: June 05, 2009, 09:08:41 AM »

Someone please educate me on the need to let the genset warm up before applying a load.

Again, I come from the boating world and it is normal practice to start the genset and hit it with everthing at once.


It's debatable just how much "warm up" is required before applying the load.  However, at a bare minimum, you want the engine to be fully started and the RPMs to stabilize first.  With no delay whatsoever, many transfer switches will close while the starter is still spinning, thus loading the engine before it has even fully started.  This puts additional strain on the starter as well as the pistons and other engine components.  Also, since voltage will not be fully up to nominal, any induction loads will actually be harder to start and draw more current, providing even more resistance and also reducing the life of those induction motors.

BTW, many marine generator installations that I have seen do include such a delay mechanism, even if it is as simple as a contactor in-line which will not close until a minimum voltage has been reached.  But almost every marine genset comes with instructions to let the generator fully start (and/or warm up) before applying the loads, so the assumption is that this will, at minimum, be done manually if there is no automatic delay.

-Sean
http://OurOdyssey.BlogSpot.com
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« Reply #32 on: June 05, 2009, 01:09:35 PM »

OK, that makes better sense. Most of the boats I have dealt with (30 to 60 feet) all have manual transfer switches so there is no issue with the genset not getting up to RPM.

Thanks for the clearing that up.
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« Reply #33 on: June 05, 2009, 09:57:01 PM »

I must confess that when the Uke goes on one of his rants I tune out a lot - maybe all - of what he is saying.  The gist of the rant was that the block is iron and the pistons are aluminum and therefore they warm up at different rates and more importantly expand at different rates.  That meant that by putting it to work too soon I was doing something that he could detect on the pistons but beyond that I don't remember. 
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