Test and Measurement Tool Users Community - Control transformer, grounding?

#21

06-30-2008, 05:41 PM

76nemo

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Re: Control transformer, grounding?

Quote:

Originally Posted by miketrek

Hey NTKBO
Thanks for the quotes from the NEC, not having one here help to see the likeness between CEC and NEC. All in all though, this was an OLD installation and the transformer was not grounded-after having a little talk with the boss, he didn't seem to think that a control trany really didnt need a ground. But in the long run, even if codes allow you not to install one, still helps you when trouble shooting!

We spoke of this before Mike. It seems from your conversation that sometimes a bond is allowed after the first disconnect. Our neutrals and earth is meant to be seperated at the first disco with little exception. I am NOT familiar with the CEC, can you start me off on the right foot???????

#22

07-01-2008, 01:29 AM

NTKBO

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Location: San Diego

Posts: 146

Re: Control transformer, grounding?

Quote:

Originally Posted by 76nemo

It is difficult to locate info on the CEC !

I found :

Quote:

Grounding Connections for Systems and Circuits (From CEC Section 10-200.)
10-200 Current Over Grounding and Bonding Conductors
1. Where wiring systems, circuits, electrical equipment, arrestors, cable armour, conduit, and
other metal raceways are grounded as a protective measure, the grounding shall be arranged so
that there is no objectionable passage of current over the grounding conductors.
2. The temporary currents which are set up under accidental conditions while the grounding
conductors are performing their intended protective functions shall not be considered as
objectionable.
3. Where through the use of multiple grounds an objectionable flow of current occurs over
the grounding conductor,
a. One or more of the grounds shall be abandoned; or
b. The location of the grounds shall be changed; or
c. The continuity of the conductor between the grounding connections shall be suitably
interrupted; or
d. Other effective action shall be taken to limit the current.

which is part of an interesting article on LV circuits in Canada:

Quote:

One of my colleagues has a desk drawer full of I/O boards that have been burned quite severely. Why did they burn? The I/O boards are in energy-limited SELV circuits. There should be no possibility of fire.
When we closely examine the boards, we find that the ground trace from the I/O connector is the trace that was overheated. ----
If the neutral is connected to ground at more than one point, then the neutral and ground are
connected in parallel between those two points. In accordance with Kirchoff’s laws, such connection makes the ground a current carrying conductor under normal conditions! ----
Thus, the neutral current gets divided into three paths: the neutral wire, the ground wire, AND the signal ground! VOILA! Lots of amps in the signal ground wire!

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#23

07-01-2008, 07:47 AM

miketrek

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Location: Guelph, Ontario CANADA-Home of 347/600

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Re: Control transformer, grounding?

Well before I miss inform everyone-yes Only one bond to neutral at the service dissconnect or switch gear and nothing after. But for a control transformer some people choose to not bond(ground) one of the legs. In the Canadian....well the Ontario Electrical code, if you have a control transformer, you can "ground" it using the "bond" cable of the enclosure with out using another grounding rod or plate. Which is the only time you can bond the neutral after the service.

When it comes to control stuff, some times you have the option of bending the code....I guess-But from the posting seems like there are times that guys do not ground the transformer-For me I have and will ground the transformer, just for troubleshooting reasons. From the first post I was at a control panel , some 200' away from the control transformer(remote push button station) and I was checking voltage but with out the other half of the trany there, there was nothing to use as my reference.
thats all............

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#24

07-01-2008, 03:58 PM

NTKBO

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Join Date: Jun 2008

Location: San Diego

Posts: 146

Re: Control transformer, grounding?

Quote:

Originally Posted by miketrek

From the first post I was at a control panel , some 200' away from the control transformer(remote push button station) and I was checking voltage but with out the other half of the trany there, there was nothing to use as my reference.
thats all............

If I understand you this time, the proceedure you are actually looking for is to disconnect from the load, bypass the 'remote push button station', and test the voltage back at the load (where the other leg lives). Then the 'remote push button' could be tested with an Ohm Meter. Reassemble and, viola.

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#25

07-02-2008, 03:08 AM

miketrek

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Re: Control transformer, grounding?

Quote:

Originally Posted by NTKBO

Yup.......But with out doing all that-IF the trany was ground, all I would have to do is take a reading from ground(panel enclosure) to the wire on the control push button.
It was a neat panel to work on to say the least.

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