Consumer Unit / Garage Electrics

[TheTransplanter]

Hi all

I am wanting to run suitable electrics to my large garage and I will be getting an electrician in to do the work.

The electrics in the garage will need to run a large compressor, small lathe, pillar drill, pond pumps, sockets, lighting etc etc.

My plan is to have a consumer unit in the garage for the above circuits, I spoke to the last electrician I had round in passing and he recommended 16mm cable on a 63a RCD! Does that sound about right?

Im an auto electrician by trade myself, so before I get a professional round I want to have things clear in my own head, plus I have floorboards up at the moment as im fitting a new bathroom along with other plumbing work, so would make sense if I can do some of the dog work myself (ie running the cable).

So the things I want to get my head around are:


1. My consumer unit in the house appears to be full (which is the latest MK unit), so would a separate 63a garage CU next to the main unit be recommended?

2. The total run from the CU to Garage is approx 25-30mtrs, so would 16mm cable be recommended

3. Can T&E be run to a box on the outside wall to a waterproof box, and then 3 core armoured cable to the garage CU

Any help or pointers would be recommended so I have a clear idea in my head and can explain what I want better for when I get someone in

Cheers

Al

 

[Jackrae]

You need to define a "large compressor"

Single phase motors take several times their running current to get going so it essential you know what the start current will be to prevent excessive voltage loss. Anything more that a 3HP or so is going to give you headache

Then you also need to address motor loads for the lathe and the pillar drill. (these'll probably be insignificant compared to the compressor but still need accounting for)

 

[mfarrow]

1. My consumer unit in the house appears to be full (which is the latest MK unit), so would a separate 63a garage CU next to the main unit be recommended?

I would have thought a 50A fuse switch would do nicely. You don't want RCD protection at the house end if you can avoid it. Do you have an earth from the supplier? Will the cable be buried along it's route to the outside?

2. The total run from the CU to Garage is approx 25-30mtrs, so would 16mm cable be recommended

Sounds good to me. You need to bury the cable 450mm underground. Buy a trenching spade, and some marker tape. If you've nothing extraneous in the garage then a smaller size might also be OK.

3. Can T&E be run to a box on the outside wall to a waterproof box, and then 3 core armoured cable to the garage CU

I assume you mean the inside face of the outside wall? T&E cannot be exposed to the elements. Yes, I'd recommend a Wiska box, they're really well built and come with good size terminals.

Do the donkey work, i.e. trench digging, and you'll save yourself a small fortune.

 

[TheTransplanter]

You need to define a "large compressor"

Single phase motors take several times their running current to get going so it essential you know what the start current will be to prevent excessive voltage loss. Anything more that a 3HP or so is going to give you headache

Then you also need to address motor loads for the lathe and the pillar drill. (these'll probably be insignificant compared to the compressor but still need accounting for)

The compressor is a 3hp 240v single phase, the manufacturer recommends a 30amp min supply.

Pillar drill is a single phase 980W

And the lathe is only a 300W small hobby lathe

 

[TheTransplanter]

I would have thought a 50A fuse switch would do nicely. You don't want RCD protection at the house end if you can avoid it. Do you have an earth from the supplier? Will the cable be buried along it's route to the outside?


Sounds good to me. You need to bury the cable 450mm underground. Buy a trenching spade, and some marker tape. If you've nothing extraneous in the garage then a smaller size might also be OK.


I assume you mean the inside face of the outside wall? T&E cannot be exposed to the elements. Yes, I'd recommend a Wiska box, they're really well built and come with good size terminals.

Do the donkey work, i.e. trench digging, and you'll save yourself a small fortune.

Yes I do have an earth from the supplier. My CU is 17th Edition if that makes a difference?

And yes the T&E would be run on the inside to the box, and then buried armoured to the garage, infact the trench is already partly dug, I just need to pull my patio up to do the rest

So are you suggesting that the 16mm should be protected by the 100A on the house CU, and then drop it down to 50A at the garage CU?

Cheers Al

 

[Taylortwocities]

Re

So are you suggesting that the 16mm should be protected by the 100A on the house CU, and then drop it down to 50A at the garage CU?

I am so glad that you have said that

I will be getting an electrician in to do the work.

As you do not have the skills to do this yourself. So why are you asking here?

There is no 100A protection on the house CU. What makes you think there is?
How do you plan to "drop it down to 50A" at the garage CU. A big resistor, perhaps?

 

[ban-all-sheds]

The compressor is a 3hp 240v single phase, the manufacturer recommends a 30amp min supply.

You'll need permission from your DNO to use that.

 

[TheTransplanter]

So why are you asking here?

Read my first post! Im asking because I want to know. Although I plan to get someone in to do this I still want to know whats, what for my own benefit!

And as different people in every trade have different opinions on how they approach things I wanted to get an over all understanding, beforehand, and you seem to have a problem with that.

Im asking questions not stating facts! Being patronising doesn't help anything except for your ego!

 

[Taylortwocities]

There are about 10 separate considerations from BS7671 that will determine the method (and constraints) of running a sub main to a separate building.

The decision on which of the (several) options and approaches can only be determined by making a site survey and having a detailed knowledge of BS7671 - a document that runs to more than 450 pages.

This is a task that only your electrician can perform for you
because:

• he has "the knowledge"
  he will use that knowledge to determine what approach to take
  he will then do the design, installation and testing
  and then sign a document to state that everything conforms to the relavent standards

That is not practical on an Internet forum.

 

[ban-all-sheds]

Still - it was worth him posting, if he didn't already know that he can't just use that compressor without asking - could have saved him no end of grief and legal trouble.

 

[ericmark]

There are ways to reduce the start load from the compressor and as long as the neighbours lights don't dip when you start it no one is going to complain so the DNO will not know. However converting a compressor to run on an inverter is not straight forward.

Because the starting with an inverter will be slower it would need the de-loading time of the compressor altering to match and also likely the motor changing to 3 phase if it was me I would look for a smaller compressor even if I retained the receiver.

Clearly if you don't use the large compressor then cable sizes would also be reduced so first job for you is to decide what to do about the compressor. All you do hinges on the compressor.

 

[mfarrow]

So are you suggesting that the 16mm should be protected by the 100A on the house CU, and then drop it down to 50A at the garage CU?

No, usual practise will be to fuse down at the house - you cannot run directly from the DNO's fuse for more than a few meters, and definitely not with 16mm² cable.

 

[Ahtyrrell]

The compressor is a 3hp 240v single phase, the manufacturer recommends a 30amp min supply.

You'll need permission from your DNO to use that.

Of course everyone who buys these sorts of compressors has to seek explicit permission from the DNO to use there consumer device don't then

http://www.machinemart.co.uk/shop/product/details/airmaster-14150-3hp-air-compressor

http://www.machinemart.co.uk/shop/product/details/clarke-tiger-14100-3hp-portable-v-twin-air-co
http://www.ebay.co.uk/itm/Rhyas-50L...Air_Tools_and_Compressors&hash=item5af3cb1fe7

 

[TheTransplanter]

So are you suggesting that the 16mm should be protected by the 100A on the house CU, and then drop it down to 50A at the garage CU?

No, usual practise will be to fuse down at the house - you cannot run directly from the DNO's fuse for more than a few meters, and definitely not with 16mm² cable.

That's what I thought, and why I questioned it

I telephoned the same electrician who has been here before (fitted my 17th edition CU & Shower), and from his memory of my property he provisionally suggested a 63a switchfuse split with a Henley block, with 16mm T&E & SWA to a CU in the garage.

He also said he is happy for me to run the 16mm T&E from the CU to the outside wall so that I can tile my bathroom floor (garage is on the opposite side of the house to the CU) just so long as I leave plenty of cable either end. Is there anything I will need to consider when doing this apart from keeping away from heater pipes and bunching with other wires?

 

[TheTransplanter]

The compressor is a 3hp 240v single phase, the manufacturer recommends a 30amp min supply.

You'll need permission from your DNO to use that.

Of course everyone who buys these sorts of compressors has to seek explicit permission from the DNO to use there consumer device don't then

http://www.machinemart.co.uk/shop/product/details/airmaster-14150-3hp-air-compressor

http://www.machinemart.co.uk/shop/product/details/clarke-tiger-14100-3hp-portable-v-twin-air-co
http://www.ebay.co.uk/itm/Rhyas-50L...s_and_Compressors&hash=item5af3cb1fe7[/QUOTE]

Exactly, I have owned and used my compressor for over 20 years at other properties and my workshop without any issues whatsoever. And the current model comes with a sealed 13a plug! And is the older model of the compressor in your first link