Workshop - 16mm armoured from consumer unit?

[Joe2003]

Hi

Im currently designing a workshop to sit at the bottom of my garden. The run from consumer unit to the workshop unit is ~25 to 27m. I will be using CNC machines, small tig welders and large compressors in the workshop (not all at the same time) as well as lighting, a computer etc.

I want to get it right first time, so was considering 16mm core armored cable. I think this protects against the relative voltage drop over this distance. Is this overkill?

Also, I have a spare slot on my household consumer unit for the workshop (its a new unit, installed 6months ago) but I cant see 16mm armored cable suffering the tight compound curves needed for the install. Is it possible for me to extend away from the consumer unit, using 60amp+ cable to a "junction box", and then run the cable from the junction box? This would simplify the run of armored cable to the workshop as I could put the junction box in the extension? I have attached a highly professional diagram to illustrate what im talking about, the blue box being the junction box, green boxes being the consumer units.

View media item 99458
Thanks for any guidance.

 

[John D v2.0]

Yes you can so it in two parts, but you need to first calculate your maximum demand to work out what supply you need. Then you need to calculate the resistance of the cable to know if the circuit breaker or fuse etc will trip in time. And as you mentioned voltage drop.
You can always terminate the swa into your cu if it's reasonably new, and run the inner cores to the terminals.

 

[bernardgreen]

You need to notify your DNO ( Distribution Network Operator ) about the equipment you intend to use as large motors and wleders can adversely affect the supply to other properties.

 

[ban-all-sheds]

I will be using CNC machines, small tig welders and large compressors in the workshop (not all at the same time) as well as lighting, a computer etc.

Before you get too far into the design, and certainly before you make any irrevocable spending commitments, you must discuss this with your DNO. If you don't, and if your equipment causes problems for other consumers, they can and will shut you down. Your agreement with them is watertight in this respect.

I want to get it right first time, so was considering 16mm core armored cable. I think this protects against the relative voltage drop over this distance. Is this overkill?

This question makes me question whether you have the right competencies to be doing electrical design work. The calculations involved re this are hardly rocket science, and if you had done them you would know the answer, so I wonder why you haven't done them.

That's not a dig at you. I'm not competent to design an aeroplane, and whilst I don't regard that as a failing I'd rightly expect criticism if I nevertheless decided I'd go and try to design one. If you decide to set yourself up as the designer, then you have to be fully capable of doing it. If you aren't then you can hardly think it a good idea to assume that role, surely?

When you apply for Building Regulations approval, what will you tell them will be the way you intend to ensure compliance with Part P?

Also, I have a spare slot on my household consumer unit for the workshop (its a new unit, installed 6months ago) but I cant see 16mm armored cable suffering the tight compound curves needed for the install. Is it possible for me to extend away from the consumer unit, using 60amp+ cable to a "junction box", and then run the cable from the junction box? This would simplify the run of armored cable to the workshop as I could put the junction box in the extension? I have attached a highly professional diagram to illustrate what im talking about, the blue box being the junction box, green boxes being the consumer units.

When you considered the different ways to supply the workshop, what made you decide that the best one in your case was to do it from your house CU?

 

[Joe2003]

Before you get too far into the design, and certainly before you make any irrevocable spending commitments, you must discuss this with your DNO. If you don't, and if your equipment causes problems for other consumers, they can and will shut you down. Your agreement with them is watertight in this respect.



This question makes me question whether you have the right competencies to be doing electrical design work. The calculations involved re this are hardly rocket science, and if you had done them you would know the answer, so I wonder why you haven't done them.

That's not a dig at you. I'm not competent to design an aeroplane, and whilst I don't regard that as a failing I'd rightly expect criticism if I nevertheless decided I'd go and try to design one. If you decide to set yourself up as the designer, then you have to be fully capable of doing it. If you aren't then you can hardly think it a good idea to assume that role, surely?

When you apply for Building Regulations approval, what will you tell them will be the way you intend to ensure compliance with Part P?



When you considered the different ways to supply the workshop, what made you decide that the best one in your case was to do it from your house CU?

I wont be doing the electrical work, im trying to come up with a rough idea for costings.

 

[stillp]

I wont be doing the electrical work, im trying to come up with a rough idea for costings.

Your DNO might not be happy with some of the equipment you plan to use, so they might have a big impact on your costings.

 

[phatboy]

I wont be doing the electrical work, I'm trying to come up with a rough idea for costings.

Get 3 electricians to cost it out for you. Listen to what they say as they may each have different ideas on how to achieve it as there are a few options. If you are unsure then, people on here will help guide you toward the best option.

It would also be worth considering some form of emergency lighting in your workshop, if the power all went out and you were using one of your machines in the evening you would appreciate the backup light to safely stop what you were doing.

 

[ban-all-sheds]

I wont be doing the electrical work, im trying to come up with a rough idea for costings.

Then the only person(s) you can discuss this with are the ones who you ask to quote for the design.

You won't be able to "tell" an electrician what to do, only specify your functional requirements.

 

[Joe2003]

You need to notify your DNO ( Distribution Network Operator ) about the equipment you intend to use as large motors and wleders can adversely affect the supply to other properties.

Your DNO might not be happy with some of the equipment you plan to use, so they might have a big impact on your costings.

Not sure if this is being taken the wrong way. By welders I meant welder, single with a 13amp socket on the end. The CNC is a small (1.5mx1m bed) DIY/Hobby style and the compressor is a standard "machine mart" 50 liter DIY grade compressor. These all (maybe not the CNC) seem like things most people would have in a hobby workshop.

Are these still items I should notify my DNO about?

 

[bernardgreen]

Are these still items I should notify my DNO about?

Excert from Northen Powergrid connection application.

• There will not be a need to reinforce the local electricity network to provide you with the load you have requested
• Our network will not need to be moved
• There are no disturbing loads, e.g. motors, welders

When the connection to the house was first made the contract included a clause about notifying the connection of distrurbing loads.

Typically motors greater than 1kW or 1Horse power are determined as disturbing loads

 

[John D v2.0]

That does seem a tight classification, admittedly our vacuum cleaner does make the lights dim, but there are a fair few consumer items with bigger motors than that! Or is it more about fixed equipment?

 

[Joe2003]

Excert from Northen Powergrid connection application.

• There will not be a need to reinforce the local electricity network to provide you with the load you have requested
• Our network will not need to be moved
• There are no disturbing loads, e.g. motors, welders

When the connection to the house was first made the contract included a clause about notifying the connection of distrurbing loads.

Typically motors greater than 1kW or 1Horse power are determined as disturbing loads

Cool, thanks for the info. Doesnt sound like it will be as simple as I had originally thought!

 

[EFLImpudence]

One horse power is 745.7 Watts

 

[Joe2003]

That does seem a tight classification, admittedly our vacuum cleaner does make the lights dim, but there are a fair few consumer items with bigger motors than that! Or is it more about fixed equipment?

Thats what I was thinking, my Bosch Mitre saw from screwfix currently requires me to notify the DNO as it pulls 1kw on startup.

 

[stillp]

By welders I meant welder, single with a 13amp socket on the end. The CNC is a small (1.5mx1m bed) DIY/Hobby style and the compressor is a standard "machine mart" 50 liter DIY grade compressor.

The physical size doesn't matter, the electrical rating is what matters. Many 50 litre compressors have 3HP motors that will blow a 13A fuse on start-up. What rating are the motors on the CNC?