480V power wiring: wiring from hot to ground to get 277V - OK?
480V power wiring: wiring from hot to ground to get 277V - OK?
(OP)
I have a situation where there is a 480V 3-Ph 3-Wire system feeding a location with some 480V motors and controls. There is no neutral pulled so the electrician wants to wire a 277V 4.5kW resistive load (electric heater) from HOT to GROUND to get 277V at the site since there is no neutral. The heater itself is rated for 300V.
I know this is not the usual or preferred way to get 277V out of a 480V 3PH system.
What are the negative effects of using this setup (480V to GROUND = 277V)?
I know this is not the usual or preferred way to get 277V out of a 480V 3PH system.
What are the negative effects of using this setup (480V to GROUND = 277V)?






RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
It's ILLEGAL.
It's DANGEROUS.
The green ground wire is required to be a non-current carrying conductor. Any use of it for carrying load current creates voltage drop across the conductor and more or less defeats its purpose. You may also have problems with any ground fault protection tripping due to load current in the green wire.
If you really have to use a 300 V load, you can install a local step-down transformer to convert the 480 V to 277 V.
If your "electrician" is a licensed journeyman, you should report him to the IBEW local.
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
If it is truly a 480V 3 wire system, rather than a 4W system without the neutral pulled to this location, in other words if it is derived from a delta or a high impedance grounded wye, the 277V to ground is merely nominal and can range from zero to 480V (or more) depending on various system conditions. Your load would have a tendency to pull it toward zero under most conditions.
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
Would this 480V/ground connection ever have the possibility of the voltage ever going above 277V? I mean way above 277V and for an extended period of time.
Would this connection pose any threat to the equipment connected to the system?
Disregard personnel safety, ground fault protection systems.
I asked this question because the heater that was connected like this failed after a very brief test. We are assuming a mfg defect, but I wanted to examine the possibility that this connection caused the failure. Besides the connection being illegal and dangerous, I want to be able to tell this person: “You have to pull a neutral because if you wire the heater backup like you did the first time – it is going to fail because”…
Because why?
:)
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
If you have a 3 wire service, you cannot use a 277V rated device without installing a new 4 wire service transformer or a dedicated smaller delta-wye transformer just to feed that load.
As as an engineer, you should not have to say things like "Disregard personnel safety, ground fault protection systems." and "Besides the connection being illegal and dangerous, I want to be able to tell this person...", you should stop right there and stand your ground based on professional conduct. I would also do it in writing to protect myself, because it sounds as though you are working for someone who is not concerned with doing things right, just cheap.
Just my humble opinion.
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
I agree with dpc, you should tell the person "You have to pull a neutral because if you wire the heater backup like you did the first time – I'll report you to the IBEW local."
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
... the heater is equipped with its own internal ground fault protection to as a necessary means to preserve life of complete imbeciles...
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
Most important and above all it could hurt or kill someone.
My 2 cents.
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
Where is he going to get a neutral from??!!! If this is a standard Delta system, like those that commonly feed motor loads, there is no possibility of a neutral.
You need another source. Either a transformer, or look elsewhere for your power.
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?
RE: 480V power wiring: wiring from hot to ground to get 277V - OK?