Spa wiring from service block

[Jeroth]

Hi I am wiring in a 46amp spa directly from the service block.

The spa has it's own mccb etc rated at 63A.

I am using 15 meters of 10mm 3 core SWA.

Am I right in thinking all I need at the service end is an RCD and isolator straight from the service block? (as shown)

Untitled

• Jeroth
• 10 Jul 2010
• 1

Many thanks.

 

[OwainDIYer]

Don't you want a fuse in there somewhere?

 

[flameport]

No.

Where is the short circuit / overload protection for the cable?
Why have an isolator and a separate RCD?

 

[ban-all-sheds]

Really annoyed - I was sure I posted this reply hours ago...

Am I right in thinking all I need at the service end is an RCD and isolator straight from the service block? (as shown)

No - your design has no overcurrent protection for the cable.

• http://www.tlc-direct.co.uk/Book/6.1.1.htm
  
  
• http://www.tlc-direct.co.uk/Book/6.2.1.htm
  
  
• //www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
  
  
• http://www.tlc-direct.co.uk/Book/8.1.1.htm
  

 

[Jeroth]

There is overload protection on the spa end.

But I could then just swap the isolator for an mcb?

 

[1john]

It doesnt matter whats at the spa end, you need to protect the cable to it, you also need to allow for discrimination too.

 

[Steve]

There is overload protection on the spa end.

But I could then just swap the isolator for an mcb?

Yes. You could also swap the RCD for an MCB. Leave the isolator there. It provides double pole iso - an MCB only provides phase iso.

Put the RCD at the spa end.

 

[ban-all-sheds]

Yes. You could also swap the RCD for an MCB. Leave the isolator there. It provides double pole iso - an MCB only provides phase iso.

Replace the isolator & RCD with a SP & N switchfuse.

 

[Jeroth]

Are there three options then?

1. Switchfuse as ban-all said. (Although I am several years ex electrician I would have used a switchfuse)

2. Just an mcb and isolator as steve said. (There is an mcb and rccbo on the spa (not mccb as I wrongly wrote in my first post) (I was working with a newly qualified electrician who said I should use just mcb & isolator)

3. An rcd & mcb & isolator?

But not just an rcd and isolator - as this has no overload protection (an electrician quoted to install to of them like this with the swa for nearly £300)

 

[securespark]

(Although I am several years ex electrician I would have used a switchfuse)

But you said before that you were going to omit the fuse?

BTW, if your spark wanted to install it this way, don't employ him. And ring his scheme provider ASAP: he is installing contrary to 7671.

 

[Jeroth]

Securespark - The electrician with the quote talked the talk and convinced me how outdated I was with my knowledge. That's why I'm checking here.

 

[ColJack]

BTW, if your spark wanted to install it this way, don't employ him. And ring his scheme provider ASAP: he is installing contrary to 7671.

but what about 433.2.2? you can have the OCPD downstream if the cable is protected for fault currents..

433.2.2 The device protecting a conductor against overload may be installed along the run of that conductor in the part of the run between the point where a change occurs ( in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions ) and the position of the protective device has neither branch circuits nor outlets for connection of current-using equipment and fulfills at least one of the following conditions:

(i) It is protected against fault current in accordance with the requirements stated in Section 434
(ii) It's length does not exceed 3 m, it is installed in such a manner as to reduce the risk of fault to a minimum, and it is installed in such a manner as to reduce to a minimum the risk of fire or danger to persons ( see also Regulation 434.2.1 )

would the main fuse cater for that?

I would go for the switchfuse though..

 

[Spark123]

The DNO don't like you using their fuse for protection of your circuits - they quite often limit the length of meter tails to 3m too.

 

[Jeroth]

Many thanks all. Switchfuse it is.

 

[ban-all-sheds]

The MEM 100ESSCF is jolly good (can take fuses of <100A), or if you want something more compact and don't need more than 80A the MEM KMF 800.

Both available BNIB on eBay right now.