ECN Forum Forums Code Related Discussion NEC & other Code issues Ground Indicating Lights

Ground lights are not required, but they are nice to have.

I once ran into a situation where we had 460V between 2 pieces of eqpt that were about 2' apart. Not a pleasant thing to come into contact with.

I agree with you Dave- I worked with a customer who produced ice cream and they could not afford to have the ice cream stop moving through the pipe line that was refrigerated with amonia because the pipeline and the manifold would freeze solid. They could tolerate a single fault and then empty the line and clear the fault under scheduled maintenance. Jon's theory while is not popular could be used to detect faults and not shut down the system.

I'm kinda looking at the information in 250.21. In 250.21(3)d, it talks about ground detectors in the control circuit when the continuity of the control circuit is required. When you look at item number (5) there is no indication the detectiors are required. I agree with the comment that it makes sense to have them.

George,
I seems like I discussed this on another forum some time back and suggested that, if this is not already clearly included in the current code it should be added.
When it comes down to it an ungrounded delta can be so dangerous I can't believe that the NEC hasn't addressed the issue. Personally I feel strongly that some type of ground detection should be required and that a qualified person be available to address a ground detection issue. I don't think it should be screwed around with.
The NEC is specific on so many things it is interesting why they appear to be avoiding this application. Maybe it's simply a political issue.

250.21(3) is only for control circuits like those found on stamping presses.

In 2005, the last sentence of 250.21 specifically requires ground detectors on most ungrounded systems.

In previous code cycles this was only an FPN.

Guys,

I have to admit to stepping well outside of my field of experience here. Here is what I said on my first post on the topic:

I was suggesting that if, _as a design choice_, someone were to use an ungrounded system for a reason other than continuity of service, then the requirements for ground fault detection might be met in a fashion other than indicator lights. I was offering this as a situation where ground fault detection was provided, but ground fault indicating lights were not used, and this was intended simply as a proposed answer to George's original question. This was not offered up as the next latest and greatest system design

The design choice is the desire to detect and remove power from ground faults without having hundreds or thousands of amps flowing through the wiring and equipment grounding system in the event of a ground fault.

I do not know if listed devices are available that would function in this fashion. I do not know if anyone does this in NEC compliant permanent installations with this design goal in mind.

I know that normal GFCI devices are only used at 120V. So a standard GFCI breaker is out. But ground fault detection equipment certainly exists for 480V systems, people complain about GFP on this board whenever they encounter a ground fault system that is not properly coordinated. So 480V two pole and three pole ground fault detecting breakers are certainly _conceivable_ products even if you can't get them off the shelf.

-Jon

JBD- First of all thanks for the '05 reference. We here in Michigan are on the '02 so I didn't look in the '05. I personally think they should be installed but as an inspector I can only recommend and can't require them. You guys in Wiconsin are ahead of us I guess. Maybe Ed Lawry had something to say about it

George, yes I am sure Ed had lots to say about it.

Jon, Class A GFCIs (people protection) are only available up to 6mA and 240V. There are some manufacturers that make non-Class A devices for 10mA and greater currents up to 480V. There are breakers with internal GF protection but they usually start at 2A and go up from there. Most mA rated devices would not be practicle due to the normal system charging current.

One problem with your method, is there is very little ground fault current flowing as a result of the first ground. In fact there might even be less current than normal based on the amount of coupling capacitance that is "shorted out".

We use floating control circuits on our emergency fans. You want the fans to run to destruction in the event of a fire. One wire grounding won't take us out of service but you lose your safety margin if you don't detect it. I install AC ground detectors which drive a Ground OK "GOK" status relay. I also install a Power OK "POK" status relay. These are both N.O.H.C. relays. The "POK" relay is driven via control power through the local "On,Hand,Remote" switch and 2 phase loss relays from the 480V side. This gives me the ability to use POK & GOK together as a very informative dual status point where:

0,0 = Power Fail
0,1 = Hand switch off of remote or phase missing.
1,0 = Ground Fault
1,1 = Normal

It's all gravy when your ground detectors help you get other info that you needed anyway.

The down side if any, is the infrequent question, "Why am I only reading 60 VAC to ground?" I tell them that the ground detector is establishing a high impedance, half point reference, and suggest a better location for a meter probe.
Joe