The tale of two generators

[fbhwt]

Two generators, one stationary 150KW, one 200KW trailer mounted, stationary generator is connected to 3pole automatic transfer switch, trailer mounted generator is back feeding load side of 400amp breaker (double lug) on stationary generator. There is a #10awg green wire connected to the frame of the trailer mounted generator, the other end is connected to the equipment ground lug on the stationary generator, anyone see any problems with this?

 

[Dennis Alwon]

So there is no utility power. You have a 200kw genny feeding a 150 kw but it is not going thru the transfer switch??

 

[fbhwt]

So there is no utility power. You have a 200kw genny feeding a 150 kw but it is not going thru the transfer switch??

Utility power connected to transfer switch, stationary gen connected to transfer switch, trailer mounted gen connected to load side breaker of stationary gen.

 

[kwired]

What happens when someone messes up with operating the generator breaker(s) and connects them together - whether one or both are running?

Code compliant or not I think is good design idea to use equipment that ensures they are in phase with one another if connected in parallel, or a second transfer switch so only one or the other can connect to the utility transfer switch at any given time.

 

[fbhwt]

What happens when someone messes up with operating the generator breaker(s) and connects them together - whether one or both are running?

Code compliant or not I think is good design idea to use equipment that ensures they are in phase with one another if connected in parallel, or a second transfer switch so only one or the other can connect to the utility transfer switch at any given time.

Should have included that the stationary gen is broke, the breaker is being used as connection point to the automatic transfer switch in the building being served. This is something that was done by another shop. I would think that the trailer mounted gen EGC would be sized according to 250.122, not sure what the #10awg is for.

 

[zbang]

Assuming the generators are not wired as separately-derived and that there is a proper SBJ in the PoCo service, the only things that come to mind are that 10g is too small for an EGC, a tag-out on the broken gen's breaker, and possibly lifting the line-side leads off that same breaker (as a double safety).

I think the 10g wire is more of a fuse, not an EGC.

 

[fbhwt]

Assuming the generators are not wired as separately-derived and that there is a proper SBJ in the PoCo service, the only things that come to mind are that 10g is too small for an EGC, a tag-out on the broken gen's breaker, and possibly lifting the line-side leads off that same breaker (as a double safety).

I think the 10g wire is more of a fuse, not an EGC.

The existing generator and transfer switch(three pole) connected to utility, not separately-derived, everything sized to existing generator.

 

[fbhwt]

Update

Update

Two generators, one stationary 150KW, one 200KW trailer mounted, stationary generator is connected to 3pole automatic transfer switch, trailer mounted generator is back feeding load side of 400amp breaker (double lug) on stationary generator. There is a #10awg green wire connected to the frame of the trailer mounted generator, the other end is connected to the equipment ground lug on the stationary generator, anyone see any problems with this?

Some things have changed in the past couple of days:
1) #10awg changed to #6awg, I am being told that the generator is grounded properly according to 250.34
2) Grounding electrode added
3) Ohmic test done between trailer and grounding electrode. This is what was said:As with grounding terminal connections, proper bonding of the neutral terminal of a power receptacle may be confirmed via testing by a
competent electrician with the correct equipment, and the ohmic resistance should measure near zero and must not be intermittent, which indicates a loose connection.
Below is the testing required for the neutral to ground to verify the ohms. Here is the result of our Ohm test on the 6AWG wire. (0.04 Ohms)
Picture shows someone with meter going from trailer to electrode.
4)I am being told that the grounding is secure, this is what was said:Issue 1: The generator not being properly grounded. According to 29CFR 1926.404(f) on the issue of grounding we see that the a portable generator according to paragraph (b) in the standard. Here is an excerpt from the standard as mentioned

"(i) Portable generators. Under the following conditions, the frame of a portable generator need not be grounded and may serve as the grounding electrode for a system supplied by the generator:

(B) The noncurrent-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame."

Over and above of the standard, the temporary generator is securely connected to the earth ground on the permanently mounted generator which has been grounded according to NEC standards for fixed installation. The temporary generator grounding is secure, independent of the additional earth ground that was placed according to the regulations, but it is not required.

Issue 2: The generator is not properly bonded. The manufacturer has made sure to bond the internal parts of the generator to the frame that covers the other concern.

 

[fbhwt]

200kw generator(trailer mounted) connected to 150kw generator pad mounted, 800amp breaker on trailer mounted generator feeding load side 400amp breaker on pad mounted generator via 4/0 type "W" portable power cable. One 4/0 cable per phase, would it be permissible to feed the line side 400amp breaker with the 800amp?