18th edition question

[cliffed]

Had these on the 18 th exam,confused me a bit.
What’s the maximum Rcd that can be used ,when an Earth electrode Reading is 2 ohms.
100 ma
300 ma
30 ma.
What would you say is the answer.

 

[telectrix]

deleted

 

[telectrix]

with a fault current of 115A, what do you think will trip i 200mS or less?

 

[cliffed]

Yea I know,told we didn’t need calculators,but putting that aside,what logical answer would it be.

 

[cliffed]

with a fault current of 115A, what do you think will trip i 200mS or less?

I’m asking,I’ve already ticked the answer,so just wondering logically,what do you reckon.

 

[telectrix]

300mA , but somewhere I recall BS7671 or a GN recommending 100mA for a TT installation ( presumably to allow for variations in the Ra)

 

[westward10]

Is that actually a genuine 18th Ed question or something from online.

 

[Loki]

Could they be relating to this table on page 64



but from memory i thought you used a 100mA RCD on TT & then 30mA at board.

 

[Loki]

Also found this on page 156

 

[telectrix]

now that is interesting. the bit about insulated and sheathed cables meeting the requirements of double or reinforced insulation.

 

[cliffed]

Is that actually a genuine 18th Ed question or something from online.

Yea,I actually ticked the 300 ma,being the max,obviously the ideal would be the 30ma.

 

[cliffed]

Also found this on page 156

View attachment 45943

Yea that is interesting,20 amp?

 

[telectrix]

Yea,I actually ticked the 300 ma,being the max,obviously the ideal would be the 30ma.

nope. you'd have 30mA for final circuits. if you had a 30mA for fault protection, that would contravene the division of circuits and discrimination of RCDs in series.

 

[cliffed]

Passed the exam,thought it was relatively hard,& you will need the 2hrs.

 

[cliffed]

nope. you'd have 30mA for final circuits. if you had a 30mA for fault protection, that would contravene the division of circuits and RCDs in series.

Yea ,agree just panicked I think,it’s the max,then churned me up

 

[telectrix]

at my age, i won't be taking the 18th, but if it was anything like 17th, i'd finished in 50 minutes, scored 87%, and that was at the age of 65. i could have done a bit better if i'd taken the time to look a couple of things up, but the pub was open.

 

[westward10]

Yea that is interesting,20 amp?

You can get an rcd shunt trip that can be set for a range of currents up into the amps.

 

[telectrix]

You can get an rcd shunt trip that can be set for a range of currents up into the amps.

never seen one of them.

 

[cliffed]

at my age, i won't be taking the 18th, but if it was anything like 17th, i'd finished in 50 minutes, scored 87%, and that was at the age of 65. i could have done a bit better if i'd taken the time to look a couple of things up, but the pub was open.

Yea this will be the last I do,done 14,15,16,17 th,this was the most difficultist,its the new regs that disturb you.

 

[Derrick Winn]

Well I am th same started in 1971 14th edition did not do anything else until part P came in, and then it's been nothing but pay out for courses books schemes . But now at nearly 63 decided to quit. Have had enough