18 th Edition questions

[Jonathan Swift]

There are two questions that Ive been unable to locate in the regs book;

1. If the line conductor is 10mm2, the min size of of an associated Surge Protection Device connection conductor is?

2. A 230 V 30 A radial circuit is protected by a BS 3036 device. If the value of earth loop impedance for the circuit is 2.3@ (I think means amps?), disconnection under line/earth fault condtion will occur in:

2s, 4s, 5s, 3s?

Thanks

 

[Dustydazzler]

Found this video about SPDs quite informative, and might cover your question iirc

 

[Andy78]

Not sure on 1 as i'm not at my book.

For 2 you need to use the supplied values to work out the prospective fault current and use the tables in appx 3 to find the answer.

 

[Dustydazzler]

As for the second question it will be ohms and ohms law

You will need to find the time curve chart for the actual tabulated trio times for 3036 fuses

 

[Wilko]

Hi - take a look at Reg 534.4.10 for SPD conductor sizes .

 

[Jonathan Swift]

Not sure on 1 as i'm not at my book.

For 2 you need to use the supplied values to work out the prospective fault current and use the tables in appx 3 to find the answer.

Many thanks, so @ was in fact Ohms and not Amps. 230/2.3 = 100. In tables is 3 seconds. Cheers

 

[Jonathan Swift]

I have done, on page 170. But it doesnt correspond to the apparent correct answer on the exam paper...

 

[Jonathan Swift]

the exam paper states 4mm, 6mm, 10mm or 2.5mm. With the correct answer apparently being 4mm

 

[Dustydazzler]

I feel a John Ward moment coming on and wanting to pass 100a through a 3Oa fuse wire to see how long it takes to blow...

I bet it’s a dang sight longer than a few seconds

 

[Andy78]

Many thanks, so @ was in fact Ohms and not Amps. 230/2.3 = 100. In tables is 3 seconds. Cheers

I'll take your word for that as not with my book to see the tables ... but sounds good.
Annoying misprint, but maybe it is to do with a technical error with software not recognised the ohm symbol. What study material are you using ?

 

[Jonathan Swift]

Ive used quite a few but these two are from sparky facts online page. Thanks for your help, I'm wondering if the second question is just the wrong answer

 

[Andy78]

Ive used quite a few but these two are from sparky facts online page. Thanks for your help, I'm wondering if the second question is just the wrong answer

Thought it might be that site. It's full of errors and out of date questions and answers. Best avoided.

 

[Wilko]

the exam paper states 4mm, 6mm, 10mm or 2.5mm. With the correct answer apparently being 4mm

Hi - yes, I thought that might happen. The reg clearly states the connection to MET is a minimum of 6mm and 2.5mm min for the live. The live size used depends on the circuit overload protective device, which you are not given. If it was 32A, I’d pick 6mm etc. With the Wylex board mounted SPD they provide 16mm (edit - maybe 10mm, brain fade sorry) for all connections.