Need clarification

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JohnnyBoy718

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new york city
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Electrician
Hello. My idiot foreman slash PM has tasked me with installing a hot water heater with a small pump. The heater is 3phase 480. The pump is 1phase 120 that draws nothing. I'm feeding the heater from an empty switch on an MCC board. What I was instructed to do is bring to bring 480 (3# 10's + 20 amp fuses) over to heater and to use one of the 277 legs to feed small step down transformer to feed pump. The problem I face is the primary side of the transformer requires a neutral. There is no neutral to be had in the MCC board it is only 3phase 480. The idiot I work is telling me to ground the neutral on the primary side of transformer. Any thoughts ???
 
I would tell him to get someone else to do it or buy a 480 volt primary transformer (tranny).
 
other option is to pull a neutral.

I wouldn't connect it to the EGC either.

If the heater is wye connected one thing that will work is to connect the transformer from one line to the wye point of the heater.

ETA:I take that back, it will work if the heating element were always on, but the pump wouldn't have any voltage whenever the thermostat isn't calling for heat, so it probably doesn't work out for the application.
 
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It's harder to find a single phase transformer with a 277V primary than it is to find one with a 480V primary by the way.

I thought it was illegal to use the EGC as a neutral, because you are making it a CCC?
 
JohnnyBoy718 said:
Hello. My idiot foreman slash PM has tasked me with installing a hot water heater with a small pump. The heater is 3phase 480. The pump is 1phase 120 that draws nothing. I'm feeding the heater from an empty switch on an MCC board. What I was instructed to do is bring to bring 480 (3# 10's + 20 amp fuses) over to heater and to use one of the 277 legs to feed small step down transformer to feed pump. The problem I face is the primary side of the transformer requires a neutral. There is no neutral to be had in the MCC board it is only 3phase 480. The idiot I work is telling me to ground the neutral on the primary side of transformer. Any thoughts ???
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What exact transformer is he asking you to install? You need a 480 - 120/240V single phase transformer of the correct kva for the pump. Period. End of story. Connect 2 277V legs on the primary to get your 480V primary; you do not need a neutral on the primary side.

btw, it's "water heater".
 
JFletcher said:
What exact transformer is he asking you to install? You need a 480 - 120/240V single phase transformer of the correct kva for the pump. Period. End of story. Connect 2 277V legs on the primary to get your 480V primary; you do not need a neutral on the primary side.

btw, it's "water heater".
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secondary side does not need 240 volts capability:angel:
 
JFletcher said:
I'm aware of that, it's just that most 1ph 480V to 120V xfmrs do both secondary voltages and are cataloged that way.
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A control transformer may not, and may be suitable for the application. Hot water circulation pump I'm guessing possibly only needs 50 maybe 100 VA transformer.
 
JohnnyBoy718 said:
I know its illegal , but what about it is unsafe ? I know your putting potential on the ground.
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When current flows through a conductor there is voltage drop on that conductor. Shorter length of conductor maybe not that much but there is still some resistance in the conductor. When you have current flowing in exposed metal parts it will raise the potential of those items and anything bonded to them over earth and other objects that are at earth potential but not bonded to the items that are carrying current. This is why you can go to almost any premises wiring system and measure from the bonded objects to a probe out in the yard and at least measure a couple volts. Around swimming pools and similar things that is way too much and the reason they have all the equipotential bonding rules they have for those applications.

The next reason is if you open the return path you are left with full circuit voltage between the components where the circuit was opened. Take a machine or appliance that is using the equipment ground to carry some of it's current and have some accidental opening of the EGC, this leaves all the metal parts bonded to the EGC at 120 volts or even 277 to other grounded objects, unless there is incidental bonding going on, then you may never notice but you still have current flowing via any path it finds rather then a designated grounded conductor.
 
JohnnyBoy718 said:
I know its illegal , but what about it is unsafe ? I know your putting potential on the ground.
Click to expand...

Again, you do not need a neutral on the primary side, nor need to use the ground as a neutral. 480 - 120V 1ph xfmrs of the kva rating you need (perhaps 100VA as kwired mentioned) are cheap, less than a hundred dollars.

Short of pulling a neutral that you dont need, and cant connect to the MCC anyway, your other option is a 480V 1 or 3ph pump, which will probably cost more than buying a small step down xfmr and 120V pump.
 
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