Trailered 3-phase generator: How many conductors needed for power cable?

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Jon456

Senior Member
Location
Colorado
We have a 240/120V 3-phase diesel generator rated at 60kW/75kVA (stand-by) and 55kW/68kVA (prime). The rated standby amps is listed at 180A, and the output breaker is 200A. The generator is mounted inside a trailer.

We need to be able to connect this to an equipment shed for back-up power in the event of a power outage. The shed has 240V 3-phase 200A service. There is a transfer switch for the 3 phase lines; the neutral is NOT switched (so the generator is not separately derived). Inside the generator, there is a label stating: "NEUTRAL bonded to FRAME."

I have an Appleton 200A 4W/4P Powertite pin & sleeve receptacle and mating plug. Both of these have a small internal tab (with threaded hole) that is mounted inside and screwed to the aluminum housing of the plug/receptacle. Presumably, this is a bonding lug, but it is very small compared to the size of the terminal lugs for the primary conductors.

I need to source some flexible cable for making the power cable between the generator and the equipment shed service. I am planning to use Type W Portable Power Cable. I think I only need 4 conductor cable: one for each of the 3 phases + one neutral. Is that correct, or do I also need a separate ground conductor?
 

Jon456

Senior Member
Location
Colorado
To comply with the NEC you will need to switch the neutral or lift the bond in the generator.
The transfer switch only switches the three hot phases; the neutral is not switched. So I guess that means I must remove the bond from the neutral in the generator.

That also means I must have an EGC in the power cable for bonding the portable generator to the service panel. Correct? But that would mean a 5-conductor Type W cable, and as far as I know, all five conductors -- including the green -- would be 3/0. (Why is it manufactured that way, instead of a #6 green wire?) And how do I make the connection between a 3/0 ground wire and the shell lug inside the Powertite plug?
 

iwire

Moderator
Staff member
Location
Massachusetts
The transfer switch only switches the three hot phases; the neutral is not switched. So I guess that means I must remove the bond from the neutral in the generator.

One or the other has to change.

That also means I must have an EGC in the power cable for bonding the portable generator to the service panel. Correct?

Yes

But that would mean a 5-conductor Type W cable, and as far as I know, all five conductors -- including the green -- would be 3/0.

I don't think that is the case with all rubber covered but I could be wrong.
 

Jon456

Senior Member
Location
Colorado
I don't think that is the case with all rubber covered but I could be wrong.
I sure hope not. That cable would be a beast and it would be impossible to connect the ground wire to the shell lug inside the Powertite plug. (Btw, I just checked the Appleton catalog again to make sure I didn't get the wrong part and I didn't. The only items they offer for 200A 3-phase with neutral are the 4W/4P plugs and receptacles with shell lug for ground.)

So can anyone point me in the right direction for a 200A power cable with 4 current carrying conductors and a reduced-size ground wire?
 

iwire

Moderator
Staff member
Location
Massachusetts
Thinking on this more I would likely use single conductor portable power cable with camloc connectors.

5-3/0 is going to be impossible to handle.



pct_368909.jpg
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
We have a 240/120V 3-phase diesel generator rated at 60kW/75kVA (stand-by) and 55kW/68kVA (prime). The rated standby amps is listed at 180A, and the output breaker is 200A. The generator is mounted inside a trailer.

We need to be able to connect this to an equipment shed for back-up power in the event of a power outage. The shed has 240V 3-phase 200A service. There is a transfer switch for the 3 phase lines; the neutral is NOT switched (so the generator is not separately derived). Inside the generator, there is a label stating: "NEUTRAL bonded to FRAME." ..

Consider a type G 4c-1/0 with ground. Grounding conductor is 4-#7, T400.5.A.2, 75C, F column gives 181A for three current carrying conductors. Southwire is 314 lbs/100ft.


ice
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
... But that would mean a 5-conductor Type W cable, and as far as I know, all five conductors -- including the green -- would be 3/0. (Why is it manufactured that way, instead of a #6 green wire?) ...

I use this stuff a lot. Generally stick with Type G - unless I have to parallel. Then the grounding conductor is too small. Thats when one goes to Type W.

ice
 
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iwire

Moderator
Staff member
Location
Massachusetts
Southwire is 314 lbs/100ft.

I usually do temp power with 4/0 single conductor in 50' lengths. It is about a pound per foot it it sucks to handle.

I would not use 3 pound per foot cable unless I was forced at gunpoint or knew I would always have plenty of labor available at a moments notice.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
... (Btw, I just checked the Appleton catalog again to make sure I didn't get the wrong part and I didn't. The only items they offer for 200A 3-phase with neutral are the 4W/4P plugs and receptacles with shell lug for ground.) ...

Unless you have to to connect and disconnect often, I tend to go with crimped lugs, a CGB, and make the connection in a disconnect

But if you are only needing this for a few hours at a time, the camlocks bob suggested, look pretty good.

ice
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Lift the bond on the genny since you can't switch the neutral.

Consider using Cam-Lok connectors to connect it to the transfer switch. Easy to connect and no issues with the size of the ground lug. We use them all the time in the Entertainment industry, and they're rated up to 400A with the correct size of cable.



SceneryDriver
 

Jon456

Senior Member
Location
Colorado
Consider a type G 4c-1/0 with ground. Grounding conductor is 4-#7, T400.5.A.2, 75C, F column gives 181A for three current carrying conductors. Southwire is 314 lbs/100ft.
Thanks Ice. I had just been looking at Type G, but thought I needed larger. I assume you chose size 1/0 because the generator's rated standby output is only 180A. Is that correct? So I can size to that instead of sizing to the generator's 200A OCPD?

As for the grounding conductors, the 4-#7 means there are four #7 ground wires in the cable bundle, correct? Do I try to lug them all together at the plug's shell connector? Four #7 wires would be the equivalent of one #1 wire, so it might still be cumbersome to make that shell connection.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
I usually do temp power with 4/0 single conductor in 50' lengths. It is about a pound per foot it it sucks to handle.

I would not use 3 pound per foot cable unless I was forced at gunpoint or knew I would always have plenty of labor available at a moments notice.

Yes, that's mostly true.

1C-4/0, type W is good. 1/c-#1 is rated for 195A and weighs .5lbs/foot. As long as one meets 590.4.B Exception, single conductors are okay. And some customers spec cable, and some are okay with single conductors. Mostly it has to do with area traffic.

ice
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Thanks Ice. I had just been looking at Type G, but thought I needed larger. I assume you chose size 1/0 because the generator's rated standby output is only 180A. Is that correct?
Yes

So I can size to that instead of sizing to the generator's 200A OCPD?
Your load can't be any more than that. And the 181A cable is protected by a 200A CB.

As for the grounding conductors, the 4-#7 means there are four #7 ground wires in the cable bundle, correct? Do I try to lug them all together at the plug's shell connector?
yes

Four #7 wires would be the equivalent of one #1 wire, so it might still be cumbersome to make that shell connection.
yes

Depending on the needed capacity - say the equipment shed only needs, 100A, consider mounting a 100A fused disconnect on the side of the equipment shed, pin and sleeve connector below, and using Type G 4c-#4.

Just a thought.

ice
 

Jon456

Senior Member
Location
Colorado
The camlock connectors with individual conductors look good. But we've already purchased the Powertite plug and receptacle, mounted the receptacle box, and ran the conduit to the transfer switch. It won't be fun lugging 3 lbs/foot cable (worse when you add the heavy Powertite plug), but it's manageable. The cable will only be 20' max. The upside over using the camlocks is that there is only ONE way to connect the Powertite plug to the receptacle, so no chance of someone else making a wrong connection and blowing up the generator or our equipment!
 

Jon456

Senior Member
Location
Colorado
Depending on the needed capacity - say the equipment shed only needs, 100A, consider mounting a 100A fused disconnect on the side of the equipment shed, pin and sleeve connector below, and using Type G 4c-#4.
The shed houses our two field pumps and associated controllers. The 18" pump is 40HP and rated at 100A. The 16" pump is ancient and has no nameplate, but I've measured its draw at 60A. Both have soft-start drivers. Typically, only one pump will run at a time, alternating between the two pumps. The water level controller can activate both pumps if the water level triggers the alarm float, however this feature can be disabled so that only one pump will run at a time.

In any case, I think we need to have available the full capacity of the generator.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
The shed houses our two field pumps and associated controllers. The 18" pump is 40HP and rated at 100A. The 16" pump is ancient and has no nameplate, but I've measured its draw at 60A. Both have soft-start drivers. Typically, only one pump will run at a time, alternating between the two pumps. The water level controller can activate both pumps if the water level triggers the alarm float, however this feature can be disabled so that only one pump will run at a time.

In any case, I think we need to have available the full capacity of the generator.

yes

Have you used this on a similar generator before in this application?

Even with a soft start, 40hp on a 65kw gen is a lot of starting current. And if your soft starts are electronic - that could also be a problem. I recently saw an application of a 100hp on a 150kw gen. The vendor (not the mfg) did not want to use an electronic soft start on a small gen. He wanted to use an autotransformer type.

Consider calling the S/S mfg and ask about using on a generator.

Just a thought

ice
 
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Jon456

Senior Member
Location
Colorado
Have you used this on a similar generator before in this application?

Even with a soft start, 40hp on a 65kw gen is a lot of starting current. And if your soft starts are electronic - that could also be a problem. I recently saw an application of a 100hp on a 150kw gen. The vendor (not the mfg) did not want to use an electronic soft start on a small gen. He wanted to use an autotransformer type.
One time, a nearby lightning strike took out the transformer that services our pump house and we were without power for a few days in a heavy storm. I rented a trailered generator and made a temporary connection (using Polaris connectors) to the feeders. The genny worked fine with the soft-start controllers and we were even able to run both pumps at the same time. I don't remember the exact rating of that rental generator, but I seem to recall it was the same (or very close to) the size of the generator that we since purchased.
 
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