What size Armoured cable should I use

I find it annoying because a sample question asked the maximum length then another asked a question about a 30metre lead. If its a maximum length it should be maximum or say maximum without RCD

 

Hat, Page 97 onwards. Clause 15.10.1 indent 2:
The length of an extension lead should be checked to ensure that it is not so great that the appliance performance may be affected by voltage drop. Extension leads incorporating 2.5mm are too large for standard 13 A plugs, although they may be used with BS EN 60309 industrial plugs. Additionally the length of any site-manufactured extension lead should not exceed the values shown in table 15.4 unless it is protected by an RCD witha rated residual operating current not exceeding 30 mA. The RCD should, preferably, form part of the fixed installation.

So if the lead has an RCD plug fitted the length stated in the table doesn't apply. If it is plugged in to a socket outlet that is on a circuit protected by either an RCD or RCBO the length stated in the table doesn't apply, however you can't guarantee it will always be used with sockets that are RCD or RCBO protected.

Kind regards.

 

Now the book I've got is missing theunless it is protected by an RCD witha rated residual operating current not exceeding 30 mA. The RCD should, preferably, form part of the fixed installation.

Bit, and the exam question asks what is the maximum length, not what is the maximum length unless an RCD is used..

I've got an extention lead with 2. 5 in a 13 amp plug btw. It does fit

 

There just seems no consistency between the books and questions. One question is to one book. Another question to another book.

 

You have got the Fourth Edition have you?

It is a tight squeeze and 13 A plugs are not intended for use with 2.5.

Kind regards

 

Did the third edition not mention the RCD thing?

 

Indeed, and I would automatically fail the arrangement if PAT Testing as it does not comply with BS 1363.

 

Yes, it did.

 

There were a lot of changes with the introduction of 4th Edition including moving to risk assessment for determining the retest interval, changes to the labelling etc. If you are working to the 3rd Edition you will not comply with current requirements, hence why you are struggling.

Kind regards

 

Correct. BS1363 goes no larger than 1.5.

Kind regards

 

What are the reasons for allowing a longer cable if an RCD is used?
Can it somehow prevent excessive voltage drop?

 

Hi Longboat

No it doesn't prevent voltage drop, but with a longer lead the resistance of the earth fault path is higher and may prevent the fuse blowing so under earth fault conditions it will still trip and keep you safe.

Kind regards

 

If you can't estimate loads, apply diversity then size a cable with voltage drop and the correction factors for a buried cable, top it all with will the Ze be too high (in most cases RCDs to provide backup protection for that) then I would leave it to the professionals.

 

7 pages.......

 

Yep, everyone has their own interpretation of skinning a cat....

 

That makes sense now why I'm failing questions.

I've no choice but to use 2. 5 on a plug. Authority won't allow it to be wired directly and 1. 5 would have too much voltage drop.

 

Ermmm what size armoured cable is the chap going to use?..

 

6mm

 

What's all that about Hat?..flipping eck m8..

 

What you mean what's it about. It's a temporary installation that must plug into the existing supply. I can't wire it direct its not my supply and I've no permission to add to it.