I am working power from a meter base installed by another electrician. It has the b phase in the meter base grounded to the meter can? I have not seen this before, have heard of it(corner grounded?). I thought this was old school? It is going to supply 480v 3phase to a mdp panel we installed. 600 amps. This mdp Feeds several big motors ranging from 10hp to 125hp. The larger motors have soft starts on them. I am concerned, should I be? Someone please school me on this. I wouldn't be worried so much, but the other electrician even installed bonding bushings on the PVC coming underground to the meterbase. I wonder if he knows what he's doing? Or maybe I'm missing something here. Thanks for any UFO or clarification.
Grounded b phase in a 480 system?
- Thread starter Huntxtrm
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kwired
Electron manager
- Location
- NE Nebraska
Has this been energized yet so that you can take some voltage readings to help verify exactly what you do have?
Is there three or four service conductors?
The fact that you said he used bonding bushings on PVC raceways does raise questions of what he may or may not know.
If it is a corner grounded system, they may be somewhat old school for services but are fairly common if you are using a separately derived system and are using a back fed delta-wye transformer as the source. All you have on the high voltage side of such a transformer is the three phases to connect to and you either have to ground a phase or use as an ungrounded system with ground fault detection equipment.
Otherwise it is no different than other grounded systems, except you need to forget the term "neutral" and learn the term "grounded conductor". NEC has all the requirements in the sections you are used to using all the time. The phase that is the grounded phase is also the "grounded conductor" and it is treated exactly the same as the grounded neutral is in a system that utilizes a neutral as the grounded conductor.
The grounded conductor is brought to the service equipment, bonded to the service equipment enclosure, and to any metallic enclosures on the supply side of the service equipment. When leaving the service equipment with branch circuits and feeders, you must isolate current carrying "grounded conductors" from non current carrying "equipment grounding conductors". Exactly the same thing you do if the grounded conductor happens to be a neutral conductor.
A grounded conductor can pass through circuit breakers and switches if they simultaneously open all conductors of the circuit, but a grounded conductor can not pass through a fuse as it is capable of opening while the rest of the circuit conductors remain in the circuit. This rule is not limited to grounded phase installations, but may be a little more common to see it done in those installations.
Is there three or four service conductors?
The fact that you said he used bonding bushings on PVC raceways does raise questions of what he may or may not know.
If it is a corner grounded system, they may be somewhat old school for services but are fairly common if you are using a separately derived system and are using a back fed delta-wye transformer as the source. All you have on the high voltage side of such a transformer is the three phases to connect to and you either have to ground a phase or use as an ungrounded system with ground fault detection equipment.
Otherwise it is no different than other grounded systems, except you need to forget the term "neutral" and learn the term "grounded conductor". NEC has all the requirements in the sections you are used to using all the time. The phase that is the grounded phase is also the "grounded conductor" and it is treated exactly the same as the grounded neutral is in a system that utilizes a neutral as the grounded conductor.
The grounded conductor is brought to the service equipment, bonded to the service equipment enclosure, and to any metallic enclosures on the supply side of the service equipment. When leaving the service equipment with branch circuits and feeders, you must isolate current carrying "grounded conductors" from non current carrying "equipment grounding conductors". Exactly the same thing you do if the grounded conductor happens to be a neutral conductor.
A grounded conductor can pass through circuit breakers and switches if they simultaneously open all conductors of the circuit, but a grounded conductor can not pass through a fuse as it is capable of opening while the rest of the circuit conductors remain in the circuit. This rule is not limited to grounded phase installations, but may be a little more common to see it done in those installations.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Sounds like you have a corner grounded system. This is pretty rare these days as most POCO's will no longer furnish such service. Most of the older ones I've seen used a single phase meter socket with the grounded phase connected to the "neutral" bar. Now days the few I see the POCO requires a specified 3 phase meter base with the grounded phase bonded to the meter can (like you have) and nothing gets connected to the neutral bar.
You need to be aware though that a corner grounded system is going to require that you use gear that is rated for corner grounding. To make such systems safe and NEC compliant requires a little different thinking and some important NEC items.
Just to be on the safe side, 1st thing I would do is to verify with POCO that you are connected to a delta system with no neutral.
2nd thing I would do is check with your drive/soft-start manufacturer to assure the units are compatible with a delta corner grounded system.
Then, as others have suggested, make sure your gear including the breakers are rated for such a system. Slash rated (480/277) breakers are not listed for ungrounded/corner grounded systems.
2nd thing I would do is check with your drive/soft-start manufacturer to assure the units are compatible with a delta corner grounded system.
Then, as others have suggested, make sure your gear including the breakers are rated for such a system. Slash rated (480/277) breakers are not listed for ungrounded/corner grounded systems.
no power yet. 3 service conductors.
ptonsparky
Tom
- Occupation
- EC - retired
As stated by others. Talk to POCO. Before going any further.
Ok, talked to "Oncor". The service provider. It is a corner grounded delta setup at the transformer. It is also corner grounded at the ct meter can, by the other electrician. Just improperly. I am moving his GEC from the bonding bushings to the can of the ct meter. Where it is already bonded to b phase. I am running a GEC to building steel from my first means of disconnect. Should I bond b phase There as well? This b phase conductor(which is grounded), should it be marked white through out the system? Even the feeders to my equipment? What about A and C phase? Brown/Yellow?
MBJ required at service disconnecting means.
Grounded conductor is required to be white, gray, three continuous white stripes on other than green insulation, or at the time of installation identified by a distinctive white or gray encircling marking at its terminations.
No requirement on ungrounded conductor's colors other not one of the options for grounded conductors.
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You can continue those colors... or change to any compliant means of identification.
kwired
Electron manager
- Location
- NE Nebraska
Too many people get confused by these systems. There is no "neutral" there still is a "grounded conductor". Treat it like you treat the "grounded conductor" on any other system. Bond it to all service enclosures, and separate this conductor from the "equipment grounding conductor" everywhere beyond the service equipment. Since it is a current carrying grounded conductor it is to be identified with gray or white coloring everywhere in the system. You do exactly the same thing with a grounded conductor in a system where the "neutral" is the grounded conductor.
As far as colors for A and C phase, you possibly could have local codes that dictate colors, otherwise NEC does not specify (in general) any particular color for any conductor identification except for grounded conductors and equipment grounding conductors. I think there is a place where purple is specified but it is not something most of us run into very often, and it also does mention orange for high leg phases, but also follows that with "or other effective means" or something like that, kind of takes away the mandate of using orange.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Soft starters likely will not care, but just so you know in case someone decides to change, DRIVES might. Most (if not all) VFDs are designed for Wye service and have protective MOVs or Common Mode Noise Capacitors on the incoming supply that are referenced to ground. If you use a corner grounded system or an ungrounded delta, extreme care must be taken in reading the manual to know what might need alteration to avoid damaging those devices. Some soft starter mfrs used to do that as well, but they mostly learned their lessons and changed the design concept years ago. If it's an off brand or cheap import though, you may want to make sure.
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