700kW Gen with Remote radiator

[seriouswatts]

I am designing a 480VAC 700kW emergency gen (Art 700) with a remote raditor and EG room exhaust fans for combustion air. I am planning on tapping off the line side bus of the generator for the exterior remote radiator. The radiator uses a 15Hp motor at 22amps.

My question is what size should the conductors be off the EG bus to the 40amp OCPD?
Should I follow the tap rules in Art 240.21 and base it off the main OCPD of the generator (1200amps). Wire sized for 120amps to the OCPD. Or Can I just size the conductors for the radiator OCPD at 40amps?

Thanks for any help.

 

[david luchini]

My question is what size should the conductors be off the EG bus to the 40amp OCPD?

I think 445.13 would require that these conductors be not less than 115% of the generator nameplate rated current.

 

[texie]

I am designing a 480VAC 700kW emergency gen (Art 700) with a remote raditor and EG room exhaust fans for combustion air. I am planning on tapping off the line side bus of the generator for the exterior remote radiator. The radiator uses a 15Hp motor at 22amps.

My question is what size should the conductors be off the EG bus to the 40amp OCPD?
Should I follow the tap rules in Art 240.21 and base it off the main OCPD of the generator (1200amps). Wire sized for 120amps to the OCPD. Or Can I just size the conductors for the radiator OCPD at 40amps?

Thanks for any help.

Usually you have the machine built with an extra breaker to feed a separate panel for the fan and related equipment. This makes it easy to comply with NFPA 110 requirements.

 

[John120/240]

I do not know. What circumstances would necessitate a remote radiator ? In my experience the generator would be located near the X former & main electric switch room. If installed indoors it would be on an exterior wall to facilitate exhaust & fresh air. Thanks

 

[texie]

I do not know. What circumstances would necessitate a remote radiator ? In my experience the generator would be located near the X former & main electric switch room. If installed indoors it would be on an exterior wall to facilitate exhaust & fresh air. Thanks

The reasons for a remote radiator vary, but usually because the machine has to go in a place that you can't accommodate getting that much air to and from the outside. This used to be a very common practice, but not so much anymore do to the high cost, but sometimes there are just no other viable options.
The OP's issue is that it is an Art 700 system and in turn NFPA 110 requires the power for any remote equipment required for the generator to operate must come from a tap on the line side of the generator main breaker. This is usually done by specifying a separate breaker on the generator bus for this purpose.

 

[seriouswatts]

Thank you for the responses. Yes, we are in a very tight room with a lot of equipment on the walls, in order to get the required cooling air for the radiator, we would eat up a most of the wall space (which there isn't anymore available). The remote radiator allows for only minimal combustion air in the room.
Article 445 states 115% with an exception of 100%. However for a radiator motor load of less then 40 amps, sizing conductors for 1200 is not very logical. Hence looking at the "tap rule" 240.21 if less then 10 feet, I can size to 1/10th the OCPD. Which in this case, there is techncally no circuit breaker since I am on the line side.
The generator manufacturer does not supply an optional OCPD for a remote radiator.

Thoughts?
Thanks

 

[david luchini]

Hence looking at the "tap rule" 240.21 if less then 10 feet, I can size to 1/10th the OCPD. Which in this case, there is techncally no circuit breaker since I am on the line side.
Thoughts?

IMO, you cannot use 240.21(B) Feeder Taps. The definition in 240.2 says

Tap Conductors. As used in this article, a tap conductor is defined as a conductor...that HAS overcurrent protection AHEAD of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.

In your situation, you do not have overcurrent protection ahead of the point of supply of the conductors, so you do not have a "tap." Therefore, you cannot use the feeder tap rules in 240.21(B).

I think you must comply with 240.21(G) and 445.13.

 

[ghostbuster]

I realize this deviates from the original question,but please make sure this remote rad and piping system is correctly designed (mechanically).We had a client that blew up a 750 kw. geny due to excessive head pressure on the geny seals because the rads were located 50 feet higher (on the roof with no mechanical check valve system etc.) then the geny.

 

[texie]

I realize this deviates from the original question,but please make sure this remote rad and piping system is correctly designed (mechanically).We had a client that blew up a 750 kw. geny due to excessive head pressure on the geny seals because the rads were located 50 feet higher (on the roof with no mechanical check valve system etc.) then the geny.

While I would not claim to be an expert on the mechanical side of this, I will say that my experience indicates that this is true. It is real important to carefully consider the manufacturers guidance (and they have plenty) for a given application as I have been involved in a number of these installs over the years. This can be complex and expensive and one of the reasons this is not as common place as it used to be. Much simpler to spec a package machine, but not always possible due to site conditions.