pir codes

[mkoffulham]

where can i find the reccomended ze and pscc readings and what if readings are to high
could you explain pfc/pscc what do we use it for. do c.breakers KA have alot to do with it as most are 10,000ka

 

[IQ Electrical]

What text books do you currently have access too?

If you have BS7671:2008, the On-Site Guide and Guidance Note 3 as a minimum then you will have most of what you need.

The recommended max Ze figures are from ESQCR Regulations 2002 and PFC values will vary according to the measured value of Ze.

Ie. take a Ze of 0.20 on a 1 phase 230V supply, Ohms law gives a calculated PFC of V/R = 1150A or 1.15 kA

On a 3 phase supply, the PSSC value is doubled as a 'rule of thumb' (the actual calculation would be X 1.732 but the rule of thumb errs on the side of safety).

The breaker 'type' as in B,C and D is a totally different proposition to short circuit capacity and one for another day!

 

[mkoffulham]

sorry i meant circuit breakers, not c type.

what if reading foe ze or pfc are to high
i have bs7671 and gn3

 

[IQ Electrical]

sorry i meant circuit breakers, not c type.

what if reading foe ze or pfc are to high
i have bs7671 and gn3

If Ze is higher than recommended values then the DNO should be informed (normally corroded joints etc.)

Generally the closer your installation is to the supply transformer, the higher the PFC will be and the lower the Ze
This is why PFC measurement is important because consideration must be given to the short circuit capacity of devices that are required to interrupt that (possibly) high current safely.

There is a 'loophole' in BS60439-3 that allows us to rely on the upstream device rating in certain circumstances, it was mainly to allow the UK continued use of the BS3036 fuse which has short circuit ratings as low as 1kA.

 

[mkoffulham]

so when would ou use 6ka breakers or 10 ka do you know page numbers??

 

[IQ Electrical]

so when would ou use 6ka breakers or 10 ka do you know page numbers??

The rated short circuit capacity of the device should be greater or equal to the measured PFC where the device is required to interrupt the fault current.
I'll bid you goodnight now!