how do I ground a 25V circuit?

[unsaint34]

I have 277/480 Y at work and I need to hook up an exit sign that uses 25V. So, I am planning to use a transformer, I assume 277/25V transformer.
I looked up the code book which said, I need to ground a system if it is less than 50V, and if it is fed by a supply system of more than 150V.
But, how do I system ground the secondary side, which is the exit sign? Run a grounding wire to concrete? Even if I did that, what do I connect it to? All the electrodes, the building metal structure, and water pipes are being used as electrodes for the building.

Am I wrong about the code?

Jon


What is the "objectionable current" at the code

 

[pierre]

Re: how do I ground a 25V circuit?

There must be a 120v supply in the building. Purchase a 120v exit light and install that.

 

[hbiss]

Re: how do I ground a 25V circuit?

I can't believe that a new 120v or 277v exit sign would cost more than a transformer and the work necessary to install it and make the 24v sign work.

-Hal

 

[peter d]

Re: how do I ground a 25V circuit?

Perhaps there is some special circumstance why this 25 volt sign is necessary.

What say you, Jon?

 

[jimwalker]

Re: how do I ground a 25V circuit?

Ok since nobody else asked i will .Why a 25 volt exit sign ? And why would it need grounded but 277 dont ?

 

[don_resqcapt19]

Re: how do I ground a 25V circuit?

Jim,
The 277 to 25 volt transformer is an SDS and requires a grounding electrode and grounding electrode conductor. This is required by 250.20(A)(1).
Don

 

[don_resqcapt19]

Re: how do I ground a 25V circuit?

Jon,

Even if I did that, what do I connect it to? All the electrodes, the building metal structure, and water pipes are being used as electrodes for the building.

You run the GEC from the transformer to the nearest available grounding electrode. It doesn't matter if that grounding electrode is already in use for another system. You many not need a GEC if you can use the exception to 250.30(A)(2), but you will need a bonding jumper. This jumper would connect to EGC for the 277 volt circuit.
Don

[ March 09, 2005, 10:39 PM: Message edited by: don_resqcapt19 ]