chenley

Say we have a 480V/3-Phase/3-Wire corner grounded Delta Meterbase.
Looking at NEC2005 250.20(B) I am reading it as stating that this system does not need to be grounded.

Then, looking at NEC2005 250.21 it is stating that this system will need ground detectors installed (which I've never heard of before).

Would it not be possible to ground the system and not require ground detectors? Just needing a little help interpreting the code.

nap

You have things mixed up.

You have a corner GROUNDED system. That means one corner is grounded. Ground fault detectors are used with UNgrounded delta systems.

micromind

Here's what I get out of those code sections. A 480 volt 3PH 3 wire system is not required to be grounded. If it is not grounded, then a ground detector is required. (They exist, I've installed them). If it is grounded, (grounded B), then the ground detector is not required.

Just my opinion, but it seems to fit.

Rob

chenley

I was thinking of just the 3 Conductors coming in from the POCO side, which that would be where they ground the B phase on the transformer bank. I would ground the meterbase the same as any other three-phase service. Am I thinking through this right?

nap

Now I'm not sure what you are asking. In may area, the meter base is grounded somtimes and sometimes it isn;t. It is a call by the POCO. Ultimately it needs to be bonded to the neutral or g e system or the EGC but how it is done varies with the POCO.

the POCO will ground one corner of the delta. You also need to bond that same corner to the GEC and associated system.

the only time you use ground fault detectors is when it is an ungrounded delta, which I have not seen installed in a long time and will not be installed in any area I work in unless there is some overwhelming need for it (in other words, they aren;t installing them anymore around here)

Basically, all of this depends on what type of service is being supplied. You need to be sure it is a corner grounded and install as needed for that. I doubt you would be looking at an ungrounded delta anymore.

chenley

It's definitely going to be a corner grounded delta. Going to call the Line Inspector tomorrow morning and verify with him about this install. Called my boss tonight and talked to him about it and we will need to install a GES. Just trying to get all my eggs in order for the quote on this one.