3 wire grounded delta service

[sevlander]

We have an existing 3 wire delta utility service with the B phase connected to ground. The connection is made in the hot service trough with 2 disconnects fed off of it. Each disconnect switch only breaks A and C phase and the grounded B phase goes straight through and is taped white. We are changing out one of the disconnect switches and discovered this arrangement.
I believe should both of these switches be upgraded to 3 pole fused type switches breaking all 3 legs and the white ID tape should be removed. The B phase is grounded in the hot trough only and not anywhere beyond that and I believe this is correct. Does anyone agree or have thoughts?
My understanding of grounding one leg is to have a reference point for voltage readings only and serves no other purpose, is this correct? Thanks

 

[ggunn]

We have an existing 3 wire delta utility service with the B phase connected to ground. The connection is made in the hot service trough with 2 disconnects fed off of it. Each disconnect switch only breaks A and C phase and the grounded B phase goes straight through and is taped white. We are changing out one of the disconnect switches and discovered this arrangement.
I believe should both of these switches be upgraded to 3 pole fused type switches breaking all 3 legs and the white ID tape should be removed. The B phase is grounded in the hot trough only and not anywhere beyond that and I believe this is correct. Does anyone agree or have thoughts?
My understanding of grounding one leg is to have a reference point for voltage readings only and serves no other purpose, is this correct? Thanks

I'm pretty sure that the installation is correct. The white tape denotes the grounded conductor (and the B phase is indeed grounded) and I'm pretty sure you don't want to interrupt the grounded conductor with a switch.

 

[sevlander]

But this is a 3 wire 240V service without a neutral. The grounded leg is actually a "hot" leg (B phase). I don't think any white wire belongs in this application and that all phases need disconnecting means and fusing.

 

[eprice]

But this is a 3 wire 240V service without a neutral. The grounded leg is actually a "hot" leg (B phase). I don't think any white wire belongs in this application and that all phases need disconnecting means and fusing.

Since B phase is connected to ground, it is the grounded conductor. Section 200.6 requires the grounded conductor to be marked with white or gray. You do not have a neutral, but you do have a grounded conductor.

240.15 only requires over current protection for the ungrounded conductors. 240.22 prohibits over current devices for the grounded conductor unless the conditions are met. Even then, it does not require over current devices for the grounded conductor.

 

[ggunn]

But this is a 3 wire 240V service without a neutral. The grounded leg is actually a "hot" leg (B phase). I don't think any white wire belongs in this application and that all phases need disconnecting means and fusing.

The B phase is only hot relative to the other conductors, the same as the grounded conductor in any other configuration. The B phase is not hot as referenced to ground, hence the white or gray tape. As for fuses, what good would a fuse on the B phase do? A ground fault on the B phase wouldn't blow the fuse.

The installation is correct. It's a corner grounded system.

 

[xformer]

The B phase is only hot relative to the other conductors, the same as the grounded conductor in any other configuration. The B phase is not hot as referenced to ground, hence the white or gray tape. As for fuses, what good would a fuse on the B phase do? A ground fault on the B phase wouldn't blow the fuse.

The installation is correct. It's a corner grounded system.

That is correct... The first ground fault grounds the system ( whether accidental as in a ground fault, or intentional as in a grounded B Phase) The Next ground fault actually creates a phase to phase fault... if I remember correctly.. That is why ungrounded systems have ground fault detectors....

 

[sevlander]

All makes sense. Thanks for everyone's input. so does the white marking continue on through out the building? For example one of the disconnects tapped from the trough feeds a step down transformer primary. Does the primary get black, white , blue as the identification on it?

 

[Smart $]

All makes sense. Thanks for everyone's input. so does the white marking continue on through out the building? For example one of the disconnects tapped from the trough feeds a step down transformer primary. Does the primary get black, white , blue as the identification on it?

Grounded conductor identification with white continues throughout this system. Conductors on the secondary side of the transformer(s), typically separately derived system(s), have to be distinguished as appropriate for that system. For example, see 215.12(C).

 

[sevlander]

All good information. THANKS

 

[hurk27]

That is correct... The first ground fault grounds the system ( whether accidental as in a ground fault, or intentional as in a grounded B Phase) The Next ground fault actually creates a phase to phase fault... if I remember correctly.. That is why ungrounded systems have ground fault detectors....

This thread is about a corner grounded system not an ungrounded system, please see post 1.

 

[gjgish]

grounded delta 3wire

grounded delta 3wire

years ago we put green tape and red tape on B phase to indicate the grounded conductor.
The NEC now says grey or white only. I think it confuses many people to see a grey or white conductor in a 3 phase power circuit
Try to think of it as a grounded conductor and not a neutral

 

[Smart $]

years ago we put green tape and red tape on B phase to indicate the grounded conductor.
The NEC now says grey or white only. I think it confuses many people to see a grey or white conductor in a 3 phase power circuit
Try to think of it as a grounded conductor and not a neutral

I can't think of any Code section which prohibits you from additional marking, such as white or gray covering with a red tracer, or white/gray and red tape.

 

[squaredan]

I never worked on a Corner grounded Delta but I have worked on Delta 3 wire center tap 240v systems. I do understand the difference in the systems. I hooked machinery of 240v 3 phase and did tape the phase.. My question is on a corner grounded system, if you were to hook up the same machinery 3phase 240v would you tape one of the phases white?

Dan

 

[GoldDigger]

I never worked on a Corner grounded Delta but I have worked on Delta 3 wire center tap 240v systems. I do understand the difference in the systems. I hooked machinery of 240v 3 phase and did tape the phase.. My question is on a corner grounded system, if you were to hook up the same machinery 3phase 240v would you tape one of the phases white?

Dan

The NEC does not much care about the colors of the wire inside utilization equipment (such as motors). You connect one wire, of whatever color, from the machinery to the white or white taped line conductor.
If you want to tape that machinery wire internally with white tape the NEC is not going to stop you. But it does not require it either.

 

[squaredan]

The NEC does not much care about the colors of the wire inside utilization equipment (such as motors). You connect one wire, of whatever color, from the machinery to the white or white taped line conductor.
If you want to tape that machinery wire internally with white tape the NEC is not going to stop you. But it does not require it either.

I meant the feeder conductors to the machine, sorry if I was not clear..

 

[iwire]

I meant the feeder conductors to the machine, sorry if I was not clear..

The NEC requires grounded circuit conductors to be white or gray. So yes, if you supply a three phase machine from corner grounded delta one of those circuit conductors is required to be white.

It is critical to realize that white or gray means grounded conductor, it does not mean neutral.

 

[don_resqcapt19]

I have three comments.

First, while it is very clear that the code requires the grounded conductor of a corner grounded system to be identified per the rules in Article 200, I have never seen that in the field in my area.

Second, the easiest why to understand how to install this type of system is to think of a single phase 120/240 volt system. Even though the corner grounded delta system is a three phase system the installation is more like a single phase system. In fact, in many cases, with a close look at the labeling you can use "single phase" disconnects and panels. You do have to be careful with the voltage rating of the breakers. "Slash" rated breakers can't be used on a corner grounded system.

Third, if 3 pole fusible disconnects are used, you need a "dummy" fuse in the grounded leg.

 

[squaredan]

The NEC requires grounded circuit conductors to be white or gray. So yes, if you supply a three phase machine from corner grounded delta one of those circuit conductors is required to be white.

It is critical to realize that white or gray means grounded conductor, it does not mean neutral.

Thank you iwire for the answer.. and Yes I do understand the diff between a neutral and grounded conductor, thanks again for that info..

 

[squaredan]

I have three comments.

Second, the easiest why to understand how to install this type of system is to think of a single phase 120/240 volt system. Even though the corner grounded delta system is a three phase system the installation is more like a single phase system. In fact, in many cases, with a close look at the labeling you can use "single phase" disconnects and panels.

Your right, thats interesting, I never thought that..