700.9 B 5 generator used for peak shaving

[RayS]

investigating using emergency generator for peak shaving.

Single existing feeder is run from 50kW genny to 2nd floor ATS and distribution.

1. Would like to tap ATS feeder and add normal loads thru completely separate panelboard (still within genny capacity, coordinated so the normal loads would not take out the emergency feeder)
2. Would like to add a second, separate ATS to feed additional normal loads. ATS would operate "backwards", dropping loads on loss of normal power to provide full power to original ATS.

My reading of 709 B 5 b says it is permissible, assuming genny breaker is not considered OCP.

709 B 5
Wiring from an emergency source is permitted to supply any combination of emergency, legally required, or optional loads in accordance with the following:
(a) From separate vertical switchboard sections or from individual disconnects mounted in separate enclosures.
(b) By single or multiple feeders without overcurrent protection at the source.

Comments please?

 

[RayS]

"borrowing" emergency power for normal loads

"borrowing" emergency power for normal loads

would it be permissible to simply add a second feed for normal loads from an emergency generator, fed thru a contactor which would drop out on loss of utility power? Would this need to be an emergency grade ATS?

Comments greatly appreciated, church budget is getting hit hard with demand charges.

 

[ron]

I'm having trouble picturing the oneline diagram.
Article 700 loads and 702 loads can coexist on a common generator, but be designed for automatic load prioritization.
Wiring of the 700 and 702 loads must be kept entirely independent, per 700.(B) [2002 code].
I don't think you can have 702 loads downstream of a 700 transfer switch.

 

[RayS]

normal loads not on emer xfer switch

normal loads not on emer xfer switch

Ron, I'm with ya 100%.

The added loads would either be:
- on their own feeder upstream of the existing ATS
-or tapped from the emer feeder just before the existing ATS. I think this is permissible under 700.9 B 5 B

 

[ron]

Normally I see the emergency 700 feeder OCPD tapped ahead (upstream) of the 702 feeder OCPD at the generator.

 

[RayS]

Thanks for the replies Ron.

It seems like the emer. feed could be tapped under '08 code, but I am not certain.

There are exceptions to the "entirely separate", under #5, "...any combination (of loads) in accordance with a,b,c"

a. ...separate switchboard sections...or individual disconnects...
b. ... single or multiple feeders without OCP at the source...

I'd be off the (single) genny output breaker with both loads. This seems ok by the exception to b, if it is "...selectively coordinated..."

c. may be an issue, "...shall not originate from the same (section,pbrd or disco) as emergency.."
My thinking is this does not include the genny output cb., but I am just not sure.