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[Andy™]

quick edit by andy lol

got myself a little confused...

166 ohms is the max Zs for 300mA. but under TT, isnt fault protection now 30mA? im looking through regs now trying to find answer

dont really see what Ra of 166 had to do with it?

Fire protection should be 300mA max RCD (532.1)

 

[Lee321]

got myself a little confused...166 ohms is the max Zs for 300mA. but under TT, isnt fault protection now 30mA? im looking through regs now trying to find answer

dont really see what Ra of 166 had to do with it?

i'm not 100% but think the main switch would need to be 100ma to cover nuisance

 

[jl-heating]

Ra x I delta n _ 50

50/Ra = I delta n

50/166 = 0.3A

max = 300mA

 

[Apache]

i'm not 100% but think the main switch would need to be 100ma to cover nuisance

You mean to provide discrimination?

 

[Lee321]

You mean to provide discrimination?

also

 

[Andy™]

Ra x I delta n _ 5050/Ra = I delta n

50/166 = 0.3A

max = 300mA

looking at 411.5.3, 300mA is correct (no idea what i was thinking!)

 

[Andy™]

You mean to provide discrimination?

unfortunately, with RCD's it can be very hard to provide discrimination. unless one is a TD, a fault can easily trip both. but you may not be able to use a TD

 

[jl-heating]

covers both discrimination and nuisance.

 

[Lee321]

covers both discrimination and nuisance.

as post #25

 

[Lee321]

unfortunately, with RCD's it can be very hard to provide discrimination. unless one is a TD, a fault can easily trip both. but you may not be able to use a TD

true but you will have satisfied the regulation by fitting it

 

[Apache]

also or a.k.a

I don't think nuisance tripping and discrimination are the same thing!

 

[Andy™]

I don't think nuisance tripping and discrimination are the same thing!

neither do i!

 

[jl-heating]

i cant find my 17th osg, is there any problem with using my old 1 for reference in the practical . ????

not much has changed really its just for tables etc ..

 

[Lee321]

I don't think nuisance tripping and discrimination are the same thing!

neither do i!

i disagree but i'm hoping to be enlightened

its a nuisance if a fault on a circuit takes out its protective device and a device further down stream (discrimination) so they go hand in hand wouldn't you say

 

[Andy™]

isnt nuisance under normal conditions and discrimination incase of fault. so fault tripping would be lack of discrimination. nuisance would be too many computers on 1 RCD with high earth leakage

 

[jl-heating]

i dont think they are the same either .. but that means nothing .

 

[Apache]

its a nuisance if a fault on a circuit takes out its protective device

No - that's supposed to happen! It's a nuisance when a fault on one circuit knocks out another (eg fault on ring - you loose the lights, fall down stairs looking for CU)

 

[Lee321]

isnt nuisance under normal conditions and discrimination incase of fault. so fault tripping would be lack of discrimination. nuisance would be too many computers on 1 RCD with high earth leakage

to the letter Applaud Smiley

 

[Lee321]

No - that's supposed to happen! It's a nuisance when a fault on one circuit knocks out another (eg fault on ring - you loose the lights, fall down stairs looking for CU)

thats what i wrote ROTFWL

 

[Andy™]

No - that's supposed to happen! It's a nuisance when a fault on one circuit knocks out another (eg fault on ring - you loose the lights, fall down stairs looking for CU)

it is a nuisance, but its because of a fault and lack of discrimination!