zs

[Farmelectrics]

trying to explain to a client this but havent got books with me please someone refresh me were does the 50v come from this formula


zs for an rcd = 50v divided by 0.03 (30mamp) = 1667 ohms

 

[Farmelectrics]

hope ive got that right ha ha no books with me

 

[Leesparkykent]

50 volts is the touch voltage

 

[Farmelectrics]

thanks lee were does the 50v come from though i no this but cant for the life of me remember

 

[Leesparkykent]

It's in reference to 1667 maximum Zs to allow a maximum 50v touch voltage during fault conditions when protected by a 30ma RCD

 

[driverman]

trying to explain to a client this but havent got books with me please someone refresh me were does the 50v come from this formula


zs for an rcd = 50v divided by 0.03 (30mamp) = 1667 ohms

LOl bit technical telling a client that sort of info! Just say it's like a car seat belt, it's there for when and if it all goes wrong.

 

[Farmelectrics]

thanks lads he was questioning why some of the test sheets he was given had codes given to high zs readings i was trying to tell him that there on rcbos and the max value becomes 1667ohms ha ha sorry i started

 

[silverfox1]

ohms law farm , now you gonna kick yourself.

 

[Farmelectrics]

yes your right silver fox ha ha just wasnt exspecting to be put on the spot bit of braine freeze lol

 

[Silly Sausage]

Is this a TT installation?

 

[driverman]

ohms law farm , now you gonna kick yourself.

There is only one Ohms law to worry about and that is...........is it Ohm time yet? :auto::auto:

 

[GB.Kayak]

trying to explain to a client this but havent got books with me please someone refresh me were does the 50v come from this formula


zs for an rcd = 50v divided by 0.03 (30mamp) = 1667 ohms

The value of 50 V relates to the typical current levels that cause ventricular fibrillation in the heart of a human being and the typical resistance of the human body in 'normal' conditions. Apply V = I x R to these values and the result is the touch voltage. Theoretically the average person in normal circumstances should not die as a result of providing an electrical path between a metal part whose touch voltage is limited to this value and earth.

 

[telectrix]

and you should be using the Zs values for the MCBs, not the cure-all RCD. the only time a RCD should be used for fault protection is on a TT install where nobody's arsed to get a decent Ra value.

 

[Farmelectrics]

yes i totally agree tel in my opinion its very un profesional to just add an rcd or rcbo to compensate a high zs reading you should investigate why your zs reading is high but napit put it in there mag that its perfectly acceptable and im looking at it right now

 

[Engineer54]

And who the hell are Napit for FFS? The only reference you should be taking any notice of is BS7671 and it's GN's/ An article in a magazine isn't worth the paper the mag is written on!!

Think about this, ....Why bother with ADS Zs values at all, on any installation if a 30mA RCD device has been provided?? At the end of the day, RCD's on TN systems are still classed (as far as i'm aware) as ''Additional'' protection, not ''Sole or main'' protection....