Insulation Resistance test on DC cable
Insulation Resistance test on DC cable
(OP)
Hi all,
I had a question posed to me the other day which made me think. I am used to doing megger (Insulation resistance) tests on AC circuits where I have a definate ground to connect to, but what if I want to test a DC cable.
To simplify the problem I have a long straight conductor and have access to both ends (close enough to attach the megger), imagine a loop. If I connect the live to the conductor and the black test lead to the insulation (or maybe wrap a new conductor around the insulation so the clips don't damage it) at the opposite end of the cable would this give me a good IR measurement?
Am I just getting tired and not thinking straight?
John
I had a question posed to me the other day which made me think. I am used to doing megger (Insulation resistance) tests on AC circuits where I have a definate ground to connect to, but what if I want to test a DC cable.
To simplify the problem I have a long straight conductor and have access to both ends (close enough to attach the megger), imagine a loop. If I connect the live to the conductor and the black test lead to the insulation (or maybe wrap a new conductor around the insulation so the clips don't damage it) at the opposite end of the cable would this give me a good IR measurement?
Am I just getting tired and not thinking straight?
John






RE: Insulation Resistance test on DC cable
http://www.solianiemc.com/products/emc-electricall...
RE: Insulation Resistance test on DC cable
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Me wrong? I'm just fine-tuning my sarcasm!
RE: Insulation Resistance test on DC cable
Are those all the assumptions that you will now treat as fact? Read and comprehend the question before you post.
@john_gopt
I see no errors in this methodology. It makes absolute sense to me.
RE: Insulation Resistance test on DC cable
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Me wrong? I'm just fine-tuning my sarcasm!
RE: Insulation Resistance test on DC cable
Keith Cress
kcress - http://www.flaminsystems.com
RE: Insulation Resistance test on DC cable
Like hcbflash, I agree it is necessary to understand the physcial environment of the cable. If it's shielded, then of course use shield as ground reference. If it's unshielded but runs through a conduit then you'll want to include that conduit in your ground reference. If you find it necessary/helpful to connect some other metalllic strap around the cable near the termination, that's fine… just connect that extra strap to the conduit so that both items together will form the ground reference.
Bear in mind there are two basic types of flaws you may be looking for:
type 1 - through-insulation defect somewhere along the length.
type 2 - leakage from the termination to groundplace… may track along surface of the cable to the nearest ground.
To detect type 1 ideally you'd like the outside of the cable in intimate contact with ground all along its length (ideal but difficult... use some judgement). To detect type 2 you'd like to add a strap nearer to the terminations than the location nearest the termination that might contact ground during service. The insulation resistance reading of course varies with the ground reference chosen.
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(2B)+(2B)' ?