Some pics from that hotel PIR

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I am a little worried about the id of conductors in that light terminal, brown to blue just does not look like it should go there :)

I do not think I would like to do any remedials on that installation, I would rather just rewire with the proper gear.

Why have they not used the earthing washers on the swa? They fitted them then just let the screw contact make the conection through the enclosures.

 
AFAIAA - there aren`t any.Mind, it HAS given rise to a serious issue in the PFC department - I didn`t bother testing the mains for PFC; as the top of one of the TPN busbars, 13 floors above here, had a phase to phase READING of >50KA; so I`ve prospectively got about 100KA of fault current up there. I haven`t yet considered the options to lower the value; if there are any. None of the devices, AFAICT, are capable of withstanding that.

KME
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Kevin,

The only way you can get the PFC for an install like this is from the DNO unless it is a private transformer then the dsigner will have to supply it by calculation.

The impedance of the transformer windings will come into play as will the impedance of the HV supply and many, may other factors.

The Powerpact should break 65kA as I read it so that will (should) limit your PFC to that.

At such low values of impedance giving these high fault values the undertainty of measurement especially with MF testers is significant.

The earth impedance path measurement needs to be done with high accuracy Ductor type meters capable or reading to a precision of milli-ohms as the PFC could easily heat up what appears to be conventionally sound joints.

Will have a look at the rest and think some more.

 
Kevin?

Thanks for the Pics KME.

I look forward to seeing the others Mate. :)

 
Kevin,The only way you can get the PFC for an install like this is from the DNO unless it is a private transformer then the dsigner will have to supply it by calculation.

The impedance of the transformer windings will come into play as will the impedance of the HV supply and many, may other factors.

The Powerpact should break 65kA as I read it so that will (should) limit your PFC to that.

At such low values of impedance giving these high fault values the undertainty of measurement especially with MF testers is significant.

The earth impedance path measurement needs to be done with high accuracy Ductor type meters capable or reading to a precision of milli-ohms as the PFC could easily heat up what appears to be conventionally sound joints.

Will have a look at the rest and think some more.
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i'm intrested in this.

so what has to be rated at the high ka?

supposing a db was connected directly to the tranny would the mcb's need to be rated to the psc? no such mcb available so what to do?

 
you mean able to with stand pfc?so how can it be safe to have a possible higher pfc than rated on down stream cpd's
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as long as there is is something at source what can break the full PFC, then other devices can be rated lower. if there is a full PFC fault for whatever reason, the lower rated device may fail, but the device rated wont, and will open the circuit

 
i don't understand how can you break thousands of amps?

i thought pfc rating meant the item does not melt/blow up/become inoperable when x pfc is passed through it

 
Lostit:r.e your question about the three SP MCCBs - they`re feeding 3 seperate sub-boards.

KME (not a kevin in sight!)
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ok cool could have been with how bad the rest is eh

 
Lostit,

Breaking capacity of a circuit breaker / fuse is just that it is the maximum current flow that it is capable of interrupting.

The device does not have to be re-useable after the fault.

Difficult obviously with a fuse! :p

A "normal" domestic type MCB to 60898 is typically capable of interrupting a fault current of 6kA.

Fault current is limited by many things not just resistance, which is why we quote impedance on our certificates even though we actually apply a DC voltage to test, thus we only measure resistance. :eek:

Think of the typical local distribution loop, you have your local HV/LV transformer, normally a Delta/Star device.

That is the HV primary is a delta wound transformer.

The coupled secondary is a star wound device.

The HV side will have its own earthing and protection systems, these may be local, or remote depending on the DNO design. Now at this point I

 
i have read many posts on a few forums about that subject and that is by the far the best explained one i have read. thankyou

 

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