Genset/shore power switching

[John316]

Anybody have any thoughts?

We have a 240 VAC 200 amp (capable) generator we need to switch between it and 50 amp shore power. The neutral and ground are bonded at the generator. Currently we switch by moving a 50 amp pigtail between two receptacles. Therefore switching all four contact. We would like to be able to use more then 50amps when we are on the genset.

Most transfer switches switch only 2 hots and have neutrals and ground bonded together. Do all three, hot, hot, and neutral need to be switched (TPDT)? Or just both hots (DPDT)? Does it matter if using a DPDT switch that bonds all the neutrals and grounds together and only switches hots?

Thoughts?

Thanks

John

[Sean]

You MUST use a transfer switch that switches the neutrals along with both hots.  There is no safe or legal way around this.

Three-pole transfer switches are very common in these ratings, though -- more so than two-pole models.  A word of warning -- a 200-amp transfer switch is going to set you back a few hundred bucks.  Remember that your generator main breaker must not exceed the rating of the switch.

Grounds are NEVER switched -- always bonded together.

-Sean
http://OurOdyssey.BlogSpot.com

[John316]

Sean,

Thanks for confirming that. I suspected that was the case, but wanted to cover all of the options. Thanks for the warning on the cost. We want a safe solution, cost is secondary.

Do you have a particular brand that you would suggest?

Your words of wisdom are greatly appreciated. 

John

[dukegrad98]

You're driving around with a 48kw generator on board?!?!?     I thought I was over the top with my 85A/20kw unit.  Wow.  Are you running a mobile MRI center in there?   

I have a 200A switch (backup genset / grid) on my 8000-square-foot building.  It's massive, and it was several hundred dollars installed -- and it wouldn't fit in the bus basement due to height.  You've got a challenge ahead!  Keep us posted.

Cheers, John

[Brassman]

Grounds are NEVER switched -- always bonded together.

-Sean
http://OurOdyssey.BlogSpot.com

....so the generator is bonded to frame and ground when on the power cord?

[Sean]

...
Do you have a particular brand that you would suggest?
...

Not in that size... I buy on price, so long as I can verify that it is listed, properly rated, and appears to be acceptable build quality.  All the big names have these -- Square-D, Eaton, Cutler-Hammer, etc., so trolling eBay for a while might get you a deal.

...
....so the generator is bonded to frame and ground when on the power cord?

Yes -- the generator ground is required to be bonded to the coach frame with a minimum #8 bonding wire.  Also, the generator neutral will be internally bonded to generator ground -- this is the reason why the transfer switch gear must switch the neutral as well as the hots -- to ensure that the neutral connection to the generator (and thus to the frame ground) is broken when running on shore power.

-Sean
http://OurOdyssey.BlogSpot.com

[PCC]

You're driving around with a 48kw generator on board?!?!?     I thought I was over the top with my 85A/20kw unit.  Wow.  Are you running a mobile MRI center in there?   

My coach has a 50Kw diesel powered genset on board, and I have used it to run everything from concert lighting and sound, and concessions, to powering a house or two when there was a major weather related power outage. I also powered three motorhomes at an event.

I just could not turn this generator down for the price, and it fit. And, believe it or not, it is actually quiet inside when running.

[Lee Bradley]

...that's what I thought before I got hearing aids.