- Joined May 6, 2012
Hi are we supposed to tie one output wire of this transformer to equipment ground? i don't see that done in many instances. is it relevant? thanks
My exception in post #2 is outlined in NFPA79 and NFPA70 (NEC) that any control circuit that is isolated can be re-referenced to Earth GND in order to resume safe practice.There is usually no reason to connect either side of an isolated 24 volt transformer winding to "ground". In fact there is not an adequate reason to connect one side of any ISOLATED power source to "ground." If there is no connection to the common ground at one side of an isolated circuit then when a grounded person contacts the other side no current will flow and no shock will be received. That is a primary reason for keeping circuit isolated from ground.
There is a large religion that believes differently and it is totally hopeless to argue with them.
What part don't you get?The mechanism of improving safety by grounding one side of an otherwise isolated circuit has not been explained in a way that makes any sense, Sort of like, If the sky fell we will be better off inside.
Max, I see where one side of the isolated decondary is connected to some variety of "ground", but tghat does not explain why assuring that one side of the circuit is a certain shock hazard relative to common ground is safer than having niether side of the circuit being a shock hazard relative to common ground.What part don't you get?
Control transformer GND re-reference
The article certainly goes into detail as to how grounding is done, but the explanation as to WHY it is done is rather nebulous. It seems far more a description of how to be like everybody else, instead of THIS is why it is important.i googled "does transformer secondary need to be grounded" and this came up. So I guess they want secondary to be ground so the circuit can trip. is that true? can't you also just put a fuse on an ungrounded secondary?
And then it’s no longer isolated because it is connected to ground via a Ground-detect lamp, which, if it is a 24V filament lamp, has quite a low resistance to ground when cold.And I am quite aware that some organizations insist on this. I also recall at least one auto plant where every control cabinet had to have "ground detect" lights to warn if either side of the isolated power had become grounded.
Totally correct, but the lamps were all Allen Bradley 800T series push to test transformer types. So the 120 volts was connected through the primary of a transformer. That meant that each side was 60 volts off ground. It also meant that no single ground would pop a fuse and stop production, as the machines were all production line items. And at the line cost of several thousand dollars per minute it made sense.And then it’s no longer isolated because it is connected to ground via a Ground-detect lamp, which, if it is a 24V filament lamp, has quite a low resistance to ground when cold.
A few more examples come to mind.i googled "does transformer secondary need to be grounded" and this came up. So I guess they want secondary to be ground so the circuit can trip. is that true? can't you also just put a fuse on an ungrounded secondary?
Some 'Organizations' include just about all Service Co. suppliers world wide for safety reasons.And I am quite aware that some organizations insist on this.
OK, I see now that it is quite a bit a "C.Y.A." practice, which certainly explains things. So I will not be attacking others "religious practices."Some 'Organizations' include just about all Service Co. suppliers world wide for safety reasons.
I suggest you get hold of a copy of 'Book on Grounding' by Eustace Soares, it is used by NEC and CEC as a reference and published by the IAEI (International Assoc. of Electrical Inspectors).
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by Jake Hertz
by Jake Hertz
by Jake Hertz