Neutral and ground 2

[Garnik]

Dear Sirs,
I have a one 3phase electrical box with 3x240 V 60Hz and one ground. I want to connect this power to one 400/000 BTU boiler and also I need 110V single phase.
I put a new ground rod near of boiler and my question is ' May I use this ground as a Neutral or Not?"
Thank you for your co-operation and helps.
With Best Regards

 

[itsmoked]

Depends on your local codes but typically you may NOT use Ground interchangeably with Neutral.

You would use a control transformer across one of your 240V-240V phase pairs to create 120V. Then you pick one side of this newly 'derived source' and ground it, running a ground wire to one side of the 120V output on the control transformer. This could be to your ground rod near the boiler.

Use this 'grounded' or 'earthed' side of the control transformer as the neutral for the 120Vac. However, you should NOT hook up to this new neutral by connecting anywhere on the 'ground wire' going to the the transformer. Hook up to the transformer directly or to a little 'neutral bus' created from the transformer's now grounded side of the 120Vac.

I hope that was all clear I repeated myself in an attempt to clarify it all and hope that didn't actually confuse you.

You most definitely need to fuse the primary of the control transformer in both of the 240V lines you're bringing to it. This is in case the transformer fails so you don't get a fire. The fuses need to conform to the safety code for selecting fuses for transformers in your location.

Also the transformer should be sized to provide the current needed for the boiler and any other 120Vac loads it needs to support. Give some thought to any future 120Vac needs that might arise as it is much less expensive to buy a bigger transformer now than to have to get another or rip this one out and replace it all with a bigger setup.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Not enough information.
First, in most ofNorth America it is against the code to use a ground connection as a neutral.
Second, there are a number of different configurations that supply phase 240 Volts. The phase to ground voltage may be different.
1> Floating delta. (ungrounded).
In a large system where the charging current is balanced and is large in relation to your load, the phase voltage to ground will be about 138 Volts.
In the event of a ground fault on another phase this voltage will approach 240 Volts.
If the system impedance to ground is not balanced, the voltage from a phase to ground may be between zero Volts and 240 Volts.
2> Delta with a zig-zag or wye-delta grounding transformer.
The voltage to ground from any phase will be 138 Volts.
3> Corner grounded delta.
The phase voltages to ground will be zero volts, 240 Volts and 240 Volts.
4> Four wire, center tapped delta.
The voltages phase to ground will be 120 Volts, 120 Volts and 208 Volts (variously called the "Wild leg", or "High Leg".
The Four wire center tapped delta system is actually quite widely used in the US.
You may have this arrangement with the neutral landed on a neutral bus in the service panel. It is quite acceptable to use one phase to this neutral bus for 120 Volts.
If you don't have a four wire center tapped delta system with a neutral brought to the panel, then you are well advised to follow itsmoked's suggestion.
Don't use a ground for a neutral.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[krisys]

Fist of all Garnik (Electrical) should tell us which region is he talking about. North American and European practices are principally different. So the answer could change depending on the region.

 

[waross]

Not much 60 Hz in Europe.

I have a one 3phase electrical box with 3x240 V 60Hz and one ground.

In distribution systems, the "Ground" connection of a transformer bank generally has a hard wired connection back to the supply source neutral in addition to multiple ground electrodes.
Although the terms "Ground" and "Neutral" are at times used interchangeably, It s not good practice to drive a ground rod and call it a neutral.

I put a new ground rod near of boiler and my question is ' May I use this ground as a Neutral or Not?"

NOT!!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Garnik]

To All of my friends,
First Merry Christ Mass and Happy New Year with my Best Wishes for all of you.
I compare your advises with my local codes and all were correct. I prepare one 4KVA transformer with 240V in primary and 120V in secondary with two fuse in primary and one fuse for secondary hot line ( I connect the ground to one side of 120v and continue as a Neutral).
Again thank you from all of you

 

[waross]

Merry Christmas and a Happy New year to you.
Thank you for the feedback. Glad to help.

Bill
--------------------
"Why not the best?"
Jimmy Carter