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Discussion Starter · #1 ·
Been taking it easy on doing electrical work for the last couple months so I'm a little rusty. Just want to make sure everything is good here. I have a commercial building with a 400A service. It's a 120/240 with a high leg. They're telling me POCO is shutting power down from 8am - 3pm on the 28th of this month, and they want me to hook up temporary power in the mean time. Generator will only be running maybe 12 hours at most. They said they'll supply the generator and cables, I am only there to hook it up. These guys know nothing about electrical, but he said the only generator he can find is 25kva. You think this would be fine for just half day temporary power. This is a poker club. They have a couple RTUs, a kitchen, bunch of tvs, not much more going on. It's been poring rain 24/7 so I haven't been able to check their amp draw. Just curious if this 25kva would most likely be fine for a 400A. That's my question, hope everyone's doing well.
 

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I'm thinking that's pretty iffy. That's a fraction of what the service is. It may work if a large portion of their service is for electric heat or A/C (depends on your location!) and is not being used this time of year.
Couple of issues:
1.How do you plan on connecting that into their system without back feeding the grid?
2. *** Do they make a 120/240 high leg generator? I could see them very easily picking up a 120/208V 3 phase generator, or a 120/240V single phase generator without knowing any better.
 

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I'm thinking that's pretty iffy. That's a fraction of what the service is. It may work if a large portion of their service is for electric heat or A/C (depends on your location!) and is not being used this time of year.
Couple of issues:
1.How do you plan on connecting that into their system without back feeding the grid?
2. *** Do they make a 120/240 high leg generator? I could see them very easily picking up a 120/208V 3 phase generator, or a 120/240V single phase generator without knowing any better.
Been there where the owner picked up a generator that was 208/120 volts for a 240/120 volt Delta service. The rental place said it would be no problem. I told him his building was set up for 240 volts and to go around and change all the taps for 6 hours was not worth it. They opted for a spider box and extension cords for the computers.
 

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Discussion Starter · #5 ·
I'm thinking that's pretty iffy. That's a fraction of what the service is. It may work if a large portion of their service is for electric heat or A/C (depends on your location!) and is not being used this time of year.
Couple of issues:
1.How do you plan on connecting that into their system without back feeding the grid?
2. *** Do they make a 120/240 high leg generator? I could see them very easily picking up a 120/208V 3 phase generator, or a 120/240V single phase generator without knowing any better.
The owner asked me these questions b/c the generator company was asking him about all this. I went back there and checked for him while I was there playing poker a few days back. I had my meter in the truck, just not a way of checking the amps at the time. It's a 120/240 3phase high leg service. So the generator company will supply a generator that works for this voltage, all that is fine and good. It's just 25kva seemed lowish to me. I'm thinking as long as each phase isn't above 80 amps I should be okay I believe?
 

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Discussion Starter · #7 ·
What can they live without during the business day short term?
Yeah I just shot the owner a text warning him about the 25kva, that I'll need to go during the heat of day tomorrow to do an amp draw to see if it's possible, but I warned him there's a chance I won't be able to run the A/C on a 25kva generator. Told him I'd confirm any suspicions tomorrow when I go and do the amp reading.
 

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Discussion Starter · #9 ·
1.How do you plan on connecting that into their system without back feeding the grid?
Oh to answer this. They have a main service disconnect outside in the back, then it penetrates into an inside gutter, and spliced and nippled into 3 different panels, all with main breakers. So I'll just turn the service disconnect off and take the load side feeder conductors off the disconnect and polaris tap to the generator cables. Everything is still protected off the main panel breakers, all panels have one.
 

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Discussion Starter · #10 ·
With a high-leg service and a 3Ø gen, the high leg will have less current on it than the other 2 therefore it can't be loaded to full capacity.
Tomorrow I'm going to do an amp reading. I'd say no more than like 75 amps per phase and I should be good with running everything off the 25kva? If it's more I'll start deleting the A/C and go from there. But no more than 75 amps per phase seems about right for maxing out the 25kva?
 

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Discussion Starter · #11 ·
Dang it I'm rusty. So now I'm questioning myself on how to ground and bond this generator properly. Here's a photo of the disconnect.
Once I shut off this disconnect which will kill utility power coming in. I'll take the 3 phases off the disconnect and polaris tap them to my 3 phase generator cables. Okay easy. Only thing I'm having a mental debate on is the neutral and ground. I guess technically the best way is to shoot a ground rod at the generator with a GEC and run a separate ground and neutral cable to the EGC and neutral going inside the building. I'm assuming this is the correct way, but I don't ever remember shooting a ground rod for whenever I used to do this back in the day when working for a company. What's an easy way to achieve the neutral and ground problem, or is that it? I'm just so sure that I never shot a ground rod with a GEC at the generator whenever I used to do this back in the day. Plus it'll be sitting on a concrete parking lot.
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If the gen is 25KVA 120/208 3Ø Y, it is good for 70 amps per leg.

Connecting a 120/208 gen to a 120/240∆ system is generally ok but you need to watch the current on the 120 legs. It's usually much higher than the high leg.
 

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Just make sure you have the right leg connected to the Delta leg of the generator. White and green either connected at the switch or the generator. They are already connected at the switch.
 

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Discussion Starter · #15 · (Edited)
Just make sure you have the right leg connected to the Delta leg of the generator. White and green either connected at the switch or the generator. They are already connected at the switch.
This is where the problem occurs for me. Every generator I've ever hooked up, if I test continuity between neutral and ground at the generator terminals with nothing hooked up, they always seem to read continuity and are internally bonded. Otherwise I'd just take off the line side neutral and my generator neutral there. But if I do that, now neutral and ground are bonded in both spots. :(

You’re going to pull the neutral when you open the disco? Is the generator 4 wire?
It'll have to be 4 wire, 3 hots and a neutral you're talking about? If not I'll have to make sure they send one that's 4 wire.
 

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Discussion Starter · #18 ·
Okay that's what I wanted to hear lol. I was thinking of just pulling out the line side neutral, cap it off, and just put the generator neutral in it's place. So I'll run 3 hots and a neutral from the generator to the disconnect. So 3 polaris taps is my material list 😁, but at $50 a tap... 😭
 

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Okay that's what I wanted to hear lol. I was thinking of just pulling out the line side neutral, cap it off, and just put the generator neutral in it's place. So I'll run 3 hots and a neutral from the generator to the disconnect. So 3 polaris taps is my material list 😁, but at $50 a tap... 😭
And phase tape! Make sure you label those wires good before you pull them off.
 
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