Inappropriate use of control transformer???

[don_resqcapt19]

I was 110% sure that any source of AC energy, no matter how many SDS's down the line, would have potential to a grounding electrode (other than capacitive coupling). It seems this isnt exactly the case. To anyone I may have offended early in this thread by relentlessly insisting there would be current to the GES, my apologies.

That is a very very common misconception. I have even seen drawings from engineers that specified only a grounding electrode, and not an EGC, for parking lot lights, based on that very same misconception.

 

[iwire]

To anyone I may have offended early in this thread by relentlessly insisting there would be current to the GES, my apologies.

I am sure no one is offended.

 

[petersonra]

there are a lot of people who believe ground rods magically make everything safe.

 

[arcsnsparks98]

I know they dont do squat for tripping breakers or blowing fuses. Unless of course its a well planned array with single digit ohm readings and then only a low amp OCP would trip. I simply was convinced that current would flow to the GES. Not much. But some none the less (excluding capacitive). I see where that is not the case. On to another issue...supplying a 15 amp receptacle from a source not capable of delivering the kVA required of a 15 amp circuit. Bad design (meaning non 508a) or actual NEC violation?

 

[petersonra]

On to another issue...supplying a 15 amp receptacle from a source not capable of delivering the kVA required of a 15 amp circuit. Bad design (meaning non 508a) or actual NEC violation?

There is no requirement that a 15A receptacle be able to supply 15A in either UL508a or the NEC. It is a design choice, neither good nor bad.

In many cases it is quite adequate for the purpose to have a 115V outlet on a 3A or 5A CB. It is often done deliberately on control panels so the CB will trip if someone hooks a vacuum cleaner to it instead of a trouble light or laptop PC that it was intended to be used for. Even if the control transformer could readily supply 15A.

 

[kwired]

Lets say I have a pretty standard 480/277v 3phase 4 wire transformer and I dont bond X0 to the GES. I Touch L1 with one finger and I touch the grounding electrode with the other, I am at no risk of electric shock?

To clarify I should have said 480/208.

Still waiting on my second cup of coffee. Sorry. X1 not L1.

If I connect X1 to the GES...hmmm, well, I have never attempted this. I would Imagine X0 would no longer be a neutral point.

I think you are starting to get it, but I will add to the conversation. Your transformer secondary is a separately derived system. There is no "ground" until you introduce one. Generally it is introduced (and usually code required) to the "neutral" of the system if there is one, but you can ground any point of the system, and that point becomes the ground reference of the system. If you had a 208/120 secondary and grounded X1 instead of X0, then you would still have 120 volts from X0 to each of X1, X2, X3, you would still have 208 volts between any two of X1,X2,X3, but voltage to ground would be zero from X1, 120 from X0, and 208 from either of X2,X3.

In your (most likely) two wire control circuit secondary, you can ground either conductor of the system, you have no ground reference until you do so. If you have an ungrounded system, then you have no ground reference at all. When a fault to ground does occur on an ungrounded system you ultimately make it a grounded system at the point of the fault. You only get fault current when a second fault occurs.

Whether or not your control circuit is permitted to be ungrounded is a different issue, but if it is - there is no current flow on any grounding elecrode conductor, or even any EGC on the first fault - all that is established with the first fault is a ground reference - any second ground fault will result in fault current flowing.

 

[iwire]

There is no requirement that a 15A receptacle be able to supply 15A in either UL508a or the NEC. It is a design choice, neither good nor bad.

That depends, if it is circuit supplying a single receptacle I agree with you.

On the other hand if they installed a duplex 210.21(B)(3) applies and the circuit size will have to match the receptacle. See Table 210.21(B)(3).

In many cases it is quite adequate for the purpose to have a 115V outlet on a 3A or 5A CB. It is often done deliberately on control panels so the CB will trip if someone hooks a vacuum cleaner to it instead of a trouble light or laptop PC that it was intended to be used for. Even if the control transformer could readily supply 15A.

I agree with you, I just don't think the NEC agrees.

 

[mbrooke]

While you are partially correct, current will absolutely flow to the GES. Most likely not a sufficient amount to clear a fault but a measurable amount of current will flow.

None will flow as its an open circuit. Ground does not soak up power. To do so without a complete circuit violates the laws of conservation.



I know it has already been explained, but adding my part nothing will flow, perhaps micro amps in relation to the primary from mutual capacitance/induction but that's it.