480/277 3 phase
- Thread starter chgeiger
- Start date
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It must be bonded, yes. Some POCOs do not allow bonding to the neutral, but through an EGC.
Either way, a single lug space is easy to work with.
Either way, a single lug space is easy to work with.
- Location
- Illinois
- Occupation
- retired electrician
EGCs do not exist on the line side of the service equipment. If you can't bond the neutral, you will need to provide a supply side bonding jumper.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Wrong term, right idea. Thanx for the correction. 
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
As others have stated, you must either bond the neutral to the enclosure or run a SSBJ. The bottom line is all metallic items must be bonded on the supply side of a service disconnect in compliance with 250.92. It is critically important for fire and shock hazards.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
I know you know understand the issue, but you know how picky some of us are about NEC terms.Wrong term, right idea. Thanx for the correction.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
How would it prevent either?
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Well, for example, if the CT enclosure is left electrically floating do to non metallic raceways it could become energized if there is a fault to the enclosure.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
How would bonding prevent a fire or shock since there is nothing upstream to trip?
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
One way or another, the transformer enclosure must be held to 0V relative to ground.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
More specifically, 0v to the supply neutral, presumed to be ground.
- Location
- Illinois
- Occupation
- retired electrician
While you can try to do that, it does not happen.
The connection to earth does not lower the voltage to earth as measured from the equipment. The connection only raises a small area of the earth around the grounding electrode to that of the equipment. If you are on top of the electrode or very close to it, the voltage to earth from the equipment will be zero. As soon as you move away from the electrode, there will almost always be some voltage, and in the case of neutral issues on the service conductor or the utility primary, this voltage can be hazardous.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Why would a CT enclosure only have one terminal for grounded conductor?
You likely have incoming and outgoing conductors in nearly all instances.
I could possibly understand a lay in lug and a single grounded conductor that passes unbroken through that lug, but around here often the POCO runs whatever they run for the supply side and the owner or his contractor runs whatever the load side may require per NEC. And with CT metering is usually large enough capacity there is multiple conductors per phase as well as multiple neutral conductors.
You likely have incoming and outgoing conductors in nearly all instances.
I could possibly understand a lay in lug and a single grounded conductor that passes unbroken through that lug, but around here often the POCO runs whatever they run for the supply side and the owner or his contractor runs whatever the load side may require per NEC. And with CT metering is usually large enough capacity there is multiple conductors per phase as well as multiple neutral conductors.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Transformers may have overcurrent devices.
Also the damage from a fault will get noticed and dealt with, thus preventing unknown shock hazard.
I agree that preventing fires is probably not a reliable benefit.hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Most do, whether it’s in a jack at the pole for a pole mount, or built in fuse holder in a pad mount. Usually over fused, but on a short circuit, usually doesn’t make much difference, it will still blow.Transformers may have overcurrent devices.
Also the damage from a fault will get noticed and dealt with, thus preventing unknown shock hazard.
- Location
- Illinois
- Occupation
- retired electrician
I have watched more than once service conductors being vaporized without the transformer primary fuse opening. In one case it was not only the service conductors, but the 4" RMC that contained the service conductors.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
FIFY. Potential will rise during a fault event.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
That is usually an arcing fault, along with poco overfusing the transformer to a point where it will destroy itself before it blows. I replaced a 4000 amp 480 volt feed where lightning struck the transformer, poco threw in larger fuses, turned it back on. 30 minutes later, the lateral was burned off down to ground level before it blew the fuses. That is why ground fault protection is used on large 480 volt systems.
- Location
- Illinois
- Occupation
- retired electrician
The utilities around here do not size to protect the transformer...they only size to prevent a transformer or secondary conductor fault from taking out the next up stream OCPD.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
larger number of customers served the more likely that may be how they do it.
I've seen enough blown primary fuses on the rural systems around here to convince me they are at least somewhat considering the transformer. Have had to set up starting delays of multiple motors in some cases to prevent blowing primary fuses, if they didn't care about protecting the transformer I'm pretty sure they could put in higher rated fuses and I wouldn't need to set up those delays.