Ground Fault Protection in Hearth Care Facilities

[jschwei314]

NEC 517.17 says one needs two levels of ground fault protection.

Does a TVSS, surgre protection equipment, breaker need GFP? The main breaker has GFP and all of the feeder breakers have GFP. Does the feeder breaker to the TVSS need GFP?

Super thanks

 

[DRWeig]

Hi, Schweitzereaton!

I fought this battle before, almost ten years ago. The guy who chaired the NEC committee on health care facilities said, "Yes." The purpose of this section of the code is to prevent a total outage due to a ground fault on any one feeder. In your case, you don't want your TVSS to fail to ground and shut down the whole shootin' match.

However, the AHJ here in Memphis said it wasn't necessary for a feeder to a single load like that to have GFP.

I would rule that you need it. I'm not your AHJ, though....

Give him a call!

Let us know what you find out...

Old Dave

 

[rbulsara]

A TVSS branch circuit protection will be a low amparage like 100A or 200A at the max.

If the GF pick up of the main is greater (for example 1200A) than the TVSS protective device rating, I don't think you need a GFP for TVSS. You may consider providing fuses for TVSS so you are assured of it clearing before the main goes. This will meet the intent of the NEC 517, imho

This is no diffrenent than say a feeder breaker of 800A rating with a GF pick up of 200A.

I can't speak for AHJs as lately I have run into some individuals with their own intepretations on some code issues..not this one in particular though. It is up to you and the Owner to pick your battles.

 

[jschwei314]

Thanks, DRWeig and rbulsara

I will do what the AHJ wants.

 

[mc5w]

First of all, a TVSS can be installed ahead of the service switch using an individual service switch. Under 2005 NEC rules this switch does not count as one of the six that are allowed on a 6 disconnect application.

If a feeder switch for a TVSS is a LOT smaller than the service so that the time current curve is not going to cross the time current curve of the service ground fault protection, that does meet the requirement for coordination of service and feeder ground fault protection in Article 517. Article 517 does not tell you how to achieve coorodination, just that you have to have it.

If your TVSS is on a 100-amp circuit breaker then the short circuit pickup is 1,000 amps for non-adjustable magnetic trip. If your circuit breaker is a 1/2 to 1 cycle pickup and clear on short circuits such as SquareD or General Electric, a plain 100-amp circuit breaker will work fine.

However, for feeders that extend farther than next to the service switchboard, there is a greater chance of ground faults in which case ground fault protection with a restraint signal sent back to the service breaker is the best method.

Mike Cole, mc5w at earthlink dot net