Fault paths question

[sudy]

Hi all,

I've a question about fault paths. I understand that the earth fault loop impedance is measured during testing so that it can be compared to the maximum value in the regs and adjusted to 80% to compensate for temperature under load conditions, but what if the fault is a short circuit ie. line to neutral, what test is done to ensure that the protective device will operate within the required disconnection time?

Thanks

 

[Brendan976]

Pscc at the incomer, look at inspection and testing sticky sum practical help it will explain all.

Ben

 

[Brendan976]

In case you can't find it
http://www.electriciansforums.net/i...tallations/17733-2391-sum-practical-help.html

 

[sudy]

Thanks a lot, much appreciated

 

[telectrix]

the EFLI values are set assuming a L-E fault of negligible impedance ( dead short ), to ensure disconnection times in the event of such a fault.

 

[HandySparks]

Hi all,

I've a question about fault paths. I understand that the earth fault loop impedance is measured during testing so that it can be compared to the maximum value in the regs and adjusted to 80% to compensate for temperature under load conditions, but what if the fault is a short circuit ie. line to neutral, what test is done to ensure that the protective device will operate within the required disconnection time?

Thanks

Good question. We make a big thing about measuring R1+R2 and Zs, to ensure that the earth fault path is of low enough impedance to operate the protective device in a short enough time. There's much less emphasis on measuring R1+Rn and Z line (line impedance). I do the Z line check at the end of the circuit at the same time as I'm doing the Zs test. If it's higher than the Zs reading, of course I'd investigate (hasn't happened yet).

Anyone know if there's a 'proper' symbol for the line impedance (like Zs for earth loop)?

 

[Golden_Boy]

Hi all,

I've a question about fault paths. I understand that the earth fault loop impedance is measured during testing so that it can be compared to the maximum value in the regs and adjusted to 80% to compensate for temperature under load conditions, but what if the fault is a short circuit ie. line to neutral, what test is done to ensure that the protective device will operate within the required disconnection time?

Thanks

Just hope the MCB or RCBO is not a chinese copy!!