Seu and 3 phase 240 volt
- Thread starter Vmadden
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I don't see how SEU would work.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
"Center phase grounded" as in the center point of a wye supply? But without the neutral being used at the equipment?
Or does that phrase mean high leg system to you?
It could even be interpreted to mean corner grounded.
Which is it?
Corner ground
Corner ground
I have always called it center phase ground, but corner ground may also be the term for it. It is a 3 phase delta 240 volt system where phase to phase is 240 volt, phase to ground is 240 volt with the exception of the center phase witch is 0 volts to ground
Corner ground
I have always called it center phase ground, but corner ground may also be the term for it. It is a 3 phase delta 240 volt system where phase to phase is 240 volt, phase to ground is 240 volt with the exception of the center phase witch is 0 volts to ground
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Agreed. But we don't know yet if the OP is referring to a corner grounded system (unlikely). I'm thinking he means a 240/120 3 phase, 4 wire system ("high leg"). Assuming this and the unit is 240 3 phase (and of course no neutral) he still needs 3 insulated conductors plus an EGC. As Don said the other day, proper terminolgy is important. As I'm sure you do, I run into this every day with electricians using wrong terminology and this leads to issues.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Sorry, I made my previous post before I saw this. Yes, it appears that you have a corner grounded system, sometimes called a grounded B phase. But you still need 3 insulated conductors and an EGC. I must say though that a NM cable wiring method is a little unusual in any place that has a corner grounded system.
Corner ground
Corner ground
Here in Baltimore city there are many of these systems still being used and many of the services are in SEU cable. The bare conductor will loop through the main ground lug and land on the center pole of the main breaker. At first glance it can look like a single phase service.
Corner ground
Sorry, I made my previous post before I saw this. Yes, it appears that you have a corner grounded system, sometimes called a grounded B phase. But you still need 3 insulated conductors and an EGC. I must say though that a NM cable wiring method is a little unusual in any place that has a corner grounded system.
Here in Baltimore city there are many of these systems still being used and many of the services are in SEU cable. The bare conductor will loop through the main ground lug and land on the center pole of the main breaker. At first glance it can look like a single phase service.
- Occupation
- Licensed Electrician
That is wild. What are they used for?
broadgage
Senior Member
- Location
- London, England
It would work fine, from a practical point of view, but would be a serious code violation since the same conductor would be being used as both a current carrying conductor to one of the motor terminals, and as an EGC.
After all, the type of cable described could AFAIK be used as the service entrance conductors, and the cable does not "know" if it is used as the service entrance, or as a branch circuit.
The NEC however makes a distinction.
The situation is somwhat similar to the use of a 3 conductor cable to supply an electric range or clothes cryer.
This used to be permitted subject to certain conditions, with same wire being used as both the neutral and the EGC, many such installations remain in use and work just fine.
The practice is now prohibited for new installations.
After all, the type of cable described could AFAIK be used as the service entrance conductors, and the cable does not "know" if it is used as the service entrance, or as a branch circuit.
The NEC however makes a distinction.
The situation is somwhat similar to the use of a 3 conductor cable to supply an electric range or clothes cryer.
This used to be permitted subject to certain conditions, with same wire being used as both the neutral and the EGC, many such installations remain in use and work just fine.
The practice is now prohibited for new installations.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I don't understand how this could be fine. A bare conductor also used as a phase conductor. Even though it is grounded there is current between phases so how could this not be dangerous? Sorry dense as usual.
kwired
Electron manager
- Location
- NE Nebraska
He said it would work fine, but then said it would be a code violation. It is in most ways no different than a single phase feeder that uses the neutral for equipment grounding. It does work, but there are associated hazards and is a code violation.
broadgage
Senior Member
- Location
- London, England
Although current passes through this conductor, it should be at ground potential and therefore safe to touch.
A bit similar to the neutral of a single phase 3 wire 120/240 volt service.
Downstream from the load center this is normally a white insulated wire.
But the uninsulated EGCs, are at the service equipment directly connected to the POCO neutral, and no one worries about touching the EGC or metal appliances connected thereto.
Until fairly recently, code permitted of the same conductor being used as both neutral and EGC for ranges and dryers. Must have been reasonably safe or it would not have been allowed for decades. It was arguably less safe than a seperate neutral and EGC that is required on new installations.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I know what he said and I know it will work. My point was from the very beginning the op was asked whether it was a corner grounded or something else. Why does it matter if it is non-compliant anyway? That was my confusion
kwired
Electron manager
- Location
- NE Nebraska
I'm going to leave it at it will work, but it is not code compliant. The primary section violated is 250.142(B).
Corner grounded
Corner grounded
I believe these services were added to existing very old single phase services in commercial buildings when 3 phase power became available in the city for large equiptment that maybe used 3 phase motors.
Corner grounded
I believe these services were added to existing very old single phase services in commercial buildings when 3 phase power became available in the city for large equiptment that maybe used 3 phase motors.
donaldelectrician
Senior Member
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Regardless of the other issues, if I recall the bare cond in seu is undersized in all sizes except 6.
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