NFPA 70E - labeling questions

[arda]

I am writing from Canada. We are trying to adapt 70E here and I have a few labelling related questions. Help will be appreciated:

1- We should label a LV panel board or switchboard where the main circuit breaker is not isolated from the rest of the equipment in such a way that we exclude the main breaker. The reason being for this is any short circuit anywhere in this panel cause the air to ionize and jump to the line side of the main protection device.
This sounds logical to me. what are your thoughts?

2- how can we differentiate between diagnostic work and live working on the equipment? What type of tasks are diagnostic?

3- We need the following documents before working on a live equipment:
a)- work permit
b)-risk assessment document
c)- work procedure
We do not need them when we do d:smile: iagnostics. Is this correct?

Thank you in advance for your help and answers

Arda PE

 

[Hassel4]

1. The protection device should clear fast enough to reduce the incident energy level and prevent an arc blast.
The other issue is one of standards. The label is to reflect the line side conductors. I would not want to confuse a worker from outside the organization not familar with the labeling method used.

2. Troubleshooting could be checking voltage levels, phase to phase phase to ground. It could involve checking loads using split CT's.

3. You should use these documents anytime workers are around exposed energized conductors. Non routine tasks should have a safe operating procedure.

My thoughts, hope it helps.

Hassel4

 

[zog]

I am writing from Canada. We are trying to adapt 70E here and I have a few labelling related questions. Help will be appreciated:

1- We should label a LV panel board or switchboard where the main circuit breaker is not isolated from the rest of the equipment in such a way that we exclude the main breaker. The reason being for this is any short circuit anywhere in this panel cause the air to ionize and jump to the line side of the main protection device.
This sounds logical to me. what are your thoughts?

2- how can we differentiate between diagnostic work and live working on the equipment? What type of tasks are diagnostic?

3- We need the following documents before working on a live equipment:
a)- work permit
b)-risk assessment document
c)- work procedure
We do not need them when we do d:smile: iagnostics. Is this correct?

Thank you in advance for your help and answers

Arda PE

1. Not really clear what you are asking here, you cant exclude anything. The main breaker is what determines the Ei for the rest of the panel, the main protects the panel and its setting determine the clearing time. Now on the line side of the main the hazard level will be different (Most likely higher) and depends on the upstream protective device. You dont assume the ionized air will flash over to the line side, any properly designed syatem should have taken that into account.

2. Not much, if the system MUST be energized to do non evasive measurements that is allowed. Voltage measurements, IR scanning, etc. You had better be able to justify your reasoning to CCOHS.

3. Correct

 

[arda]

Hassel4 and Zog,
thank you for replies.

when you say that the label should reflect the line side of the conductors, where do you see this statement? I agree with this one since this is the worst case. However the companies may say that through training the workers can differentiate where they are working and therefore two labels (one line side and one load side) are required for each cubicle. Everyone is doing differently I guess. I am trying to learn which one is the safest without overdressing the workers which may casue inadvertant accidents. There is no protection against blast and this is what worries me.

I was talking of ionization where switchboard or panel boards are being worked on. In a MCC, the main breaker is not in the same cubicle where you may be working. But when you open a panel, you see everythig located in one location not separated from each other including the main breaker. This is what I tried to say. What you are saying is regarless where the fault happens even if in the panel, the air surrounding the main breaker line side terminal should not be ionized becasue of the design. Makes sense. Is it the fact or accepted approach that I do not know and this is what I am asking.
Thank you again

 

[zog]

. What you are saying is regarless where the fault happens even if in the panel, the air surrounding the main breaker line side terminal should not be ionized becasue of the design. Makes sense. Is it the fact or accepted approach that I do not know and this is what I am asking.
Thank you again

Sort of, I am saying it should be designed that way, but I cant tell you anything for a fact based on a loose description in a discussion forum. "Switchgear" should have seperate compartments to take care of this problem by definition.

For a "Panel" that may not be true. Make sense eh?