Genset Breaker to Switchgear Grounding

D

dcreaney

Member
Location
Darien, Wi
Occupation
Electrical Engineer
Greetings,

I have a genset enclosure that has a 2500KW generator with a 4000A breaker that feeds a 4000A switchgear inside the enclosure. I am running (10) 444KCMIL DLO cables per phase and neutral and (2) 444KCMIL DLO cables per ground. The cable is routed from the genset to the switchgear in 2 layers of cable tray, (2) 444KCMIL DLO per tray. I have always sized the ground per NEC 250.66 grounding electrode conductor. I have an inspector that is saying these grounds need to be sized per NEC 250.122 (F) (1) equipment grounding conductors. So, I am curious which code would apply to this application.
 
Pet peeve here-
Are you using actual DLO (not an NEC cable type) or are you using a fine-stranded dual-listed cable that's also RHH/RHW-2? (Or why not just use THHN can be done with it? Or another NEC fine-strand type like W? If you don't need the 2kv insulation you're wasting money on it.)
 
zbang said:
Pet peeve here-
Are you using actual DLO (not an NEC cable type) or are you using a fine-stranded dual-listed cable that's also RHH/RHW-2? (Or why not just use THHN can be done with it? Or another NEC fine-strand type like W? If you don't need the 2kv insulation you're wasting money on it.)
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Using a UL listed RHH/RHW that is also TC rated.
 
OK, so you're not using DLO, you're using RHH/RHW. I'm still curios why you're using that and not some other cable.

dcreaney said:
One end at the generator and one at the switchboard.
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Where are those terminating- on a ground bus at each end or ???? (Where is the N/G bond of the system? Is there on at the generator or is it in the switchboard? Another way to look at this- is the generator a Separately Derived System or not?)
 
zbang said:
OK, so you're not using DLO, you're using RHH/RHW. I'm still curios why you're using that and not some other cable.


Where are those terminating- on a ground bus at each end or ???? (Where is the N/G bond of the system? Is there on at the generator or is it in the switchboard? Another way to look at this- is the generator a Separately Derived System or not?)
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That is the type of cable that the customer has specified for the job.

They both terminate at bus bar and the N/G bond is at the genset.
 
dcreaney said:
That is the type of cable that the customer has specified for the job.

They both terminate at bus bar and the N/G bond is at the genset.
Click to expand...
Then it sounds like the inspector has the correct termination. The conductor in question is an equipment grounding conductor running with the feeder between the generator and switchboard. The size of the equipment grounding conductor is determined by the size of the upstream overcurrent protection.
 
zbang said:
OK, so you're not using DLO, you're using RHH/RHW. I'm still curios why you're using that and not some other cable.


Where are those terminating- on a ground bus at each end or ???? (Where is the N/G bond of the system? Is there on at the generator or is it in the switchboard? Another way to look at this- is the generator a Separately Derived System or not?)
Click to expand...
A lot of DLO is dual rated as RHH?RHW.
 
My point is that it has to be dual-rated, but even calling it DLO is not really right as it's not an NEC cord type (when used for NEC applications). Or- unless you're wiring a diesel locomotive, use fine-strand RHW/RHH (or W, etc).

I guess some of my intensity is that so many people don't seem to know that W and SC exist.
 
zbang said:
My point is that it has to be dual-rated, but even calling it DLO is not really right as it's not an NEC cord type (when used for NEC applications). Or- unless you're wiring a diesel locomotive, use fine-strand RHW/RHH (or W, etc).

I guess some of my intensity is that so many people don't seem to know that W and SC exist.
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It is marked DLO/RHW/RHH. There is no reason not to call it DLO. This is the same with welding cable. There are a couple of brands that are marked welding cable/RHW/RHH.

I can get dual rated DLO much quicker than I can get Type G or Type W portable power cables.
 
Dunno, I rent large cable when needed and it's always W, never "DLO" (why pay for 2kv insulation on a 480 system?) or RHH/RHW. I suppose what's available how fast depends on where you are.

On a similar note, when someone says "welding cable", that doesn't automatically mean dual-rated RHW/RHH, there's a lot of non-NEC welding cable out there. I'd rather be more precise in my spec and I'd rather others were, too. (I also know I'm tilting at windmills on this :) .)
 
zbang said:
Dunno, I rent large cable when needed and it's always W, never "DLO" (why pay for 2kv insulation on a 480 system?) or RHH/RHW. I suppose what's available how fast depends on where you are.

On a similar note, when someone says "welding cable", that doesn't automatically mean dual-rated RHW/RHH, there's a lot of non-NEC welding cable out there. I'd rather be more precise in my spec and I'd rather others were, too. (I also know I'm tilting at windmills on this :) .)
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That is why I said there are a few brands that are dual marked.

In the real world, I see no hazard in using the products that are not dual marked.

Many years ago, I researched one brand of welding cable that offered both welding cable and dual rated welding cable. The only difference was that the non-dual rated cable had insulation that was 25% thicker then the dual rated. After that, it really didn't matter to me if it had the dual rating or not.

Most of the DLO that I have used was for large DC motors with an armature voltage exceeding 600 volts, so I did need a higher voltage insulation.
 
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