Wiring a portable standby generator

[Jon456]

We purchased a 60kW diesel generator (120/240V 3-phase delta) to provide emergency power for our storm water pumps; the generator will be trailer mounted. The service panel and the generator each have 200A OCPD/disconnects.

The manual transfer switch I've selected is a Winco/Square-D 200A 3-pole switch,
Catalog #DTU324NRB. This unit does not switch the neutral. So my understanding is that while the generator is connected to the transfer switch, then the generator is not considered a "separately derived system" and thus does not need its own GES. (However, I do need to ensure that the generator's neutral is not bonded to its ground.)

However, we will be making the connection from the generator to the pump house via a flexible cable and reverse service pin & sleeve plug/receptacle. Since this means the generator's neutral (and its phases) can be disconnected from the transfer switch, does this change the "separately derived system" status of the generator? There is no intention of operating the generator while it is not plugged into the transfer switch.

Also, what wire is typically used inside the receptacle mounting box to connect the pin & sleeve receptacle to the transfer switch. From photos, it seems that the mounting box doesn't have the depth to accommodate large gauge stranded THWN copper wire. Is it typical to use flexible wire inside these boxes?

 

[Smart $]

Being connected via plug and receptacle doesn't change the non-SDS status.

 

[Jon456]

Thanks for the clarification on SDS status.

Can anyone offer guidance on what wire is typically used from the pin & sleeve receptacle (on mounting box) to the transfer switch? Looking at the mounting box, it seems like it would be tough to get 3/0 THHN in there with enough length to make the receptacle connections while still being able to pack it back in to affix the receptacle to the box cover.

 

[augie47]

There may be a more compliant way, but what I've seen here is pre-wire the connector with "pigtails" and push them through to a j box.

 

[Jon456]

There may be a more compliant way, but what I've seen here is pre-wire the connector with "pigtails" and push them through to a j box.

I was thinking of lugging the 3/0 THHN into the receptacle terminals and then pulling the wire bundle back towards the transfer switch to get the box cover closed. Then make the terminations in the transfer switch. But that would only be practical if the conduit between the receptacle box and the transfer switch is a straight run.

I was just wondering if it was typical to use Type G-GC or Type W (or similar) flexible cable in the conduit to make the connection between the receptacle and the transfer switch.

 

[chris kennedy]

I was just wondering if it was typical to use Type G-GC or Type W (or similar) flexible cable in the conduit

Sounds like a 400.8(6) issue.

 

[qcroanoke]

There may be a more compliant way, but what I've seen here is pre-wire the connector with "pigtails" and push them through to a j box.

That's what we do.
Just go right through the back of the box to the other side of the wall into the switch or a pull box big enough to where we don't have to fight the wires into it to get it closed.

 

[don_resqcapt19]

Sounds like a 400.8(6) issue.

He can use DLO/RHW...almost exactly the same as type W power cable, but code compliant, assuming that he can find terminations suitable for the fine stranded construction of that type of cable.

 

[Jon456]

That's what we do. Just go right through the back of the box to the other side of the wall into the switch or a pull box big enough to where we don't have to fight the wires into it to get it closed.

The mounting boxes for these receptacles have a threaded hole for conduit at the top of the box. The back of the box is solid. Clearly, the manufacturers intend for the wires to be routed through conduit into the top of the box and then turn out and down to the receptacle lugs. So there must be a proper way to wire these without modifying the box by cutting a hole in the back (which won't work anyway if you are unable to penetrate the wall and mount your panels on the inside).