external office

[RobDavidson]

Hi,

I'm new, hoping for some help.

I'm planning on building an office at the end of our garden, approx 30m away - I need a bit of help with the following questions:

1) Do I have to use armoured cable if I'm not putting it underground?

2) The cable run would be between 30 and 40m so I think i need to consider voltage drop - I'll only be powering computer, heating and lights so a) what cable size should I use? b) what fuse should I use on the RCD of my supply?

Hope you can help.

Kind regards,

Rob

 

[ColJack]

read up on part P ( it's in the wiki ) and then decide if it's worth the bother of DIY, or getting a sparky in to take care of it all for you?

 

[ban-all-sheds]

1) Do I have to use armoured cable if I'm not putting it underground?

So where are you planning to put it?

2) The cable run would be between 30 and 40m so I think i need to consider voltage drop - I'll only be powering computer, heating and lights so a) what cable size should I use? b) what fuse should I use on the RCD of my supply?

Basics on the relationships between cable and fuse ratings here: http://www.diynot.com/forums/viewtopic.php?p=81696#81696

and MCB types and how/why they affect fault-loop maxima here: http://www.diynot.com/forums/viewtopic.php?p=76467#76467

A good guide to selecting cable sizes here: http://www.kevinboone.com/cableselection_web.html

This is a useful design guide, with reference tables for conductors, maximum fault-loop values etc:

http://www.amazon.co.uk/Electrical-Installation-Design-Guide-Calculations/dp/0863415504 or http://www.theiet.org/publishing/books/wir-reg/electrical-installation-design-guide.cfm

 

[Steve]

I'm planning on building an office at the end of our garden, approx 30m away

Quite a distance

I need a bit of help with the following questions:

fire away

1) Do I have to use armoured cable if I'm not putting it underground?

probably. Though it sounds like you're trying to cut corners to save money. Not the way to think out an electrical installation.

2) The cable run would be between 30 and 40m so I think i need to consider voltage drop - I'll only be powering computer, heating and lights so a) what cable size should I use? b) what fuse should I use on the RCD of my supply?

Back @ ya:
1. How much wattage heating and what variety?
2. How many lights and what wattage?
3. Anything else you havent thought of such as kettle, toaster, microwave, water heater?
4. How do you fit a fuse IN an RCD? This question makes me worry about your competence, though the fact you quote voltage drop indicates some knowledge.

 

[wingcoax]

4. How do you fit a fuse IN an RCD? This question makes me worry about your competence, though the fact you quote voltage drop indicates some knowledge.
How many times do we hear the phrase "A little knowledge is dangerous"?

 

[ericmark]

Let me assume you want to run 3Kw of heating and some other small items, which would require at least a 16A MCB on the radial plus a lighting radial at 6A, which would mean at least a 20A MCB feeding the whole lot in the house.

So at 30M this means the smallest cable you could use is 4mm², however if you wanted a 32A supply then 10mm² becomes the smallest cable. With SWA this would mean a 25mm gland. As to not using SWA it would seem penny pinching, as by time one has paid the £100 plus vat for the LABC to comply with Part P, plus posts and catenaries to support aerial cables, it would seem in most cases a better option to use SWA. Also with 6mm² and above, the better earth fault loop impedance figures, would also likely be an advantage.

I would think you would be better to employ a registered Electrician, as by time you knock off the LABC charges it is very little if any gain to DIY.

I would not consider using a fuse with anything over 13A in a household supply unless protecting semi-conductor devices. I would use a miniature circuit breaker (MCB) or a RCBO (MCB + RCD combined) because of the earth fault loop impedance requirements.

If you can keep your current below 13A then you may use a fuse but you still would need 4mm² cables so seems little point.