Branch circuit derating/Generator grounding

[Jubert Lowe]

I install 15 KW home standby generator in Boca Raton Florida my guys ground the generator and propane gas pipe just as we do in Dade County the Inspector said that the generator or the gas pipe must not be grounded.

from the pre wired transfer switch there is a 1" flex that carries three 2-pole breakers 2,30a. 1, 40a. 5, 15a 1-pole 2-20a 1-pole. the house panel is on the opposit side of the door we install a 8"x 8"x 4" J-box from that j-box to the house panel we install a 2" conduit with a # 6 netural.

 

[haskindm]

Does the transfer switch include a pole for the neutral? In other word is the neutral switched? If the neutral is solidly connected to the power company neutral (Grounded Conductor) then this is not a seperately derived system and should not have its own grounding electrode system.

 

[NoVA Comms Power]

First ... lets get the terminolgy straight.

The genset frame will ALWAYS be "grounded" ... either via the EGC in a non-SDS installation or -- as pointed out by haskindm -- a SDS is grounded via it's own grounding electrode system.

A non-SDS frame "may" have it's own supplementary grounding electode installed, but it may not serve as the sole source of grounding (remember, you'll still have the EGC) and the extra electrode provides little-to-no value in most opinions.

Second ... what the inspector may be referring to is the "neutral-to-ground" bond specifically for the genset.

A non-SDS genset must NOT have this bond; it utilizes the service's main bonding jumper to ground the genset's grounded conductor. (if it helps, think of the genset as a sub-panel where the neutrals and grounds are isolated from each other) ...

... while a SDS system must adhere to the applicable Art 250 section and WILL have a neutral-to-ground bond for the genset's grounded conductor ... with the "neutral-switching" ATS preventing a "two simultaneous N-G bonds / parallel neutral" situation.

[Edit to add] The propane pipe will be grounded by whatever method is grounding the genset frame. Be aware that there is currently a lot of "churn" re: the grounding requirements for Corregated Stainless Steel Tubing (CSST). For more info see http://forums.mikeholt.com/showthread.php?t=84103

 

[LarryFine]

The propane pipe will be grounded by whatever method is grounding the genset frame.

Can o' worms time.

Suppose the Propane tank happens to be mounted on a grounded metallic surface, such as a platform in concrete, adjacent to the building and rebar-tied? Parallel neutral-current pathway through the fuel line?

 

[NoVA Comms Power]

Parallel neutral-current pathway through the fuel line?

How?

Where are the two on-premises simultaneous N-G bonds located?

However, I agree that once current gets on the grounding system, all bets are off and "parallelism back to the source via all possible paths" is the rule.

Jim