TM and Wiring question for MEP701A/16B

[Ratch]

I found mine choked badly on a 4.5kw resistive load at 300'. I would say not to expect too much more than rated output from it. Even 4kw is still 33% higher than rated. I'd say 3.5kw and it'll stay healthy.

 

[MidKnightBomber]

Good tip Ratch!

Thank ya

I have read and heard over and over again that these are under rated as compared to civy gen sets. But needed to get a better sense on what that meant.

 

[MidKnightBomber]

My electrician is going to come over to the house to wire up the gen set in about 1-2 weeks and his argument is to wire it up as 220v to the house. I was talking to him over the phone and the connection was poor so I didn't get a solid understanding for his justification but I know it had to do with getting the proper return/neutral line. The guy is very experienced and I trust him as he has wired in a bunch of our big machinery at work but I need to talk to him in person to get a better idea why in the world he would recommend 220v?

You guys have any idea why he would recommend that? He says it doesn't affect the transfer switch that he buys.

 

[Isaac-1]

I suspect he wants to do it because it makes sense to him from an electrician point of view with concerns about under sized return neutrals, balanced loads in the breaker box, etc, but what he is likely not taking into account is the very limited capacity of this generator and how wiring it up 120/240V effectively splits it into being 2 120V generators with half the total output on each since it sounds like you have no 240V appliances that can run on the 16 amps at 240V that this generator can provide.

Let me put this in other words, wired 120/240V split single phase you are in effect getting 2 buckets of 16 amps each to draw from, instead of one bucket of 32 amps. Lets pretend you have a big chest freezer that draws 9 amps, a window air conditioner that draws 10 amps, and a refrigerator that draws 8 amps, plus a few CF light bulbs that draw less than one amp each, and maybe a modern TV that draws an amp or two, and a notebook computer that draws an amp. When wired 120V only you get a bucket of 32 amps at 120V, so 9+10+8+1+2+1 =31 amps so no problem it is under the rated 32 (real world may be 35 or so, but you get the idea). Now lets make that two buckets of 16 amps, 9+10 = 19, oopps you are over, hmmm 9+8 = 17 ooops your over again, hmmm there is no way to get there and power the fridge, freezer and air conditioner at once. For a reasonable work around to this problem see my post #8 in this thread.

 

[rustystud]

I suspect he wants to do it because it makes sense to him from an electrician point of view with concerns about under sized return neutrals, balanced loads in the breaker box, etc, but what he is likely not taking into account is the very limited capacity of this generator and how wiring it up 120/240V effectively splits it into being 2 120V generators with half the total output on each since it sounds like you have no 240V appliances that can run on the 16 amps at 240V that this generator can provide.

Let me put this in other words, wired 120/240V split single phase you are in effect getting 2 buckets of 16 amps each to draw from, instead of one bucket of 32 amps. Lets pretend you have a big chest freezer that draws 9 amps, a window air conditioner that draws 10 amps, and a refrigerator that draws 8 amps, plus a few CF light bulbs that draw less than one amp each, and maybe a modern TV that draws an amp or two, and a notebook computer that draws an amp. When wired 120V only you get a bucket of 32 amps at 120V, so 9+10+8+1+2+1 =31 amps so no problem it is under the rated 32 (real world may be 35 or so, but you get the idea). Now lets make that two buckets of 16 amps, 9+10 = 19, oopps you are over, hmmm 9+8 = 17 ooops your over again, hmmm there is no way to get there and power the fridge, freezer and air conditioner at once. For a reasonable work around to this problem see my post #8 in this thread.

I like your explanation Isaac ! Solid and to the point.

 

[pahunter]

I think the rest is correct, note that the ground jumper to the grounding point is often already installed, but is usually connected to the back side of the output lug inside the control box, not the outside connector point. Also that grounding of L-2 would be correct for a 240V only 2 wire system, but would NOT be correct for a 120/240V split single phase where you would want the neutral grounded. As to arguments against wiring it to the house in 120V only mode the biggest one tends to be the potential for under sized neutrals in your breaker box on shared return neutral circuits. If you are planning on wiring in a whole home transfer switch this might be an issue, but if you are just wiring in a transfer sub panel, you (he) can check the individual circuits for undersized neutrals as they are hooked up, and make sure not to hook any two up that share an under sized neutral. Hopefully this would not mean having to choose between hooking up the outlet for the refrigerator or hooking up the outlet for the microwave (or running a new larger neutral). If you are wiring it up to a whole house transfer switch and have under sized neutrals, an alternative compromise here is to only hook it up to one side of the box (gen L1 - house L1, gen L2 - house L0, but nothing to house L-2 in 120V 1 phase only mode, or vice versa) this would only provide power to half the outlets in the house, and might mean having to move some breakers around for all important loads to be on the powered half, but I think should work.

I’m still confused on how to get 32 amps all 120v on one line, just to have a receptacle box, not hooked up to a house