Discuss Armoured cable 16mm or 25mm in the Electrical Forum area at ElectriciansForums.net

Cliff C

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I am not an electrician. Can anyone help please?

I have an outbuilding which I am converting into two offices.

The building is currently served by a 16mm armoured cable running underground from my house, the distance is about 100 metres.

Potentially the building could have a maximum of the following appliances:-

2x2kw electric oil filled radiators
1x1.5kw electric oil filled radiator
Hand wash 2.5kw
Electric Kettle 2.5kw
Saniflo 400 watts
Vacuum Cleaner 1kw
4 Fluorescent Lights
2 Computers
Total aprox 13kw

Will the existing 16mm cable be adequate or will I have to have it replaced with a 25mm armoured cable.

Thank you
 

telectrix

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bear in mind that not all loads will be in use simultaneously. applying diversity, I'd allow for an aveage load of 8kW. that equates to c. 40A, so as far as current capacity, 16mm will,be fine. volt drop however may be a factor.
 

Strima

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For a 40 amp load over that distance you will have a volt drop of 11.2 volts.

As you have lighting the maximum permitted is 3%, 6.9 volts, even using 25mm you are just over for volt drop.

Also depending on your current earthing arrangements and protective device type you would be looking at 35mm as a minimum.

My advice is to employ the services of a local electrician to design and install this for you, a few figures and a bit of SWAG on the internet is no substitute for a full site visit and survey.
 

telectrix

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i could not be arsed to work out the VD as books are in van. however, for wtat it would cost to replace the 16mm cable versus exceeding the 3% for lighting, I'd fit LED lights which are happy with a slightly reduced voltage and sod it. at the end if the day, it's only a shed, not a hospital operating theatre. tin hat ready.
 

Spoon

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With your current 16mm cable, you can have a 25A breaker.
 

Spoon

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it's only a shed, not a hospital operating theatre.
Following on from this mate. If he is to reduce the items going into the shed then the max breaker he can have is 25A.. :kissingheart::kissingheart:
 

Pete999

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I am not an electrician. Can anyone help please?

I have an outbuilding which I am converting into two offices.

The building is currently served by a 16mm armoured cable running underground from my house, the distance is about 100 metres.

Potentially the building could have a maximum of the following appliances:-

2x2kw electric oil filled radiators
1x1.5kw electric oil filled radiator
Hand wash 2.5kw
Electric Kettle 2.5kw
Saniflo 400 watts
Vacuum Cleaner 1kw
4 Fluorescent Lights
2 Computers
Total aprox 13kw

Will the existing 16mm cable be adequate or will I have to have it replaced with a 25mm armoured cable.

Thank you
Will that be a 3 phase or Single phase supply?
 

telectrix

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Following on from this mate. If he is to reduce the items going into the shed then the max breaker he can have is 25A.. :kissingheart::kissingheart:
i'm at a loss to see why he should fit a 25A breaker protecting a 16mm cable.
 

Spoon

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i'm at a loss to see why he should fit a 25A breaker protecting a 16mm cable.
Voltage drop.
Any higher than 25A and the voltage drop would exceed 3%
 

Wilko

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Hi - 100m is a long run and as usual the heating becomes a load problem as it might be on all day.
 

telectrix

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the breaker is there to protect the cable from overload/short circuit, not to minimise volt drop. it' s Ib that should not exceed 25A, not In.
 
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Spoon

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Get yourself a wood burner and save yourself 3.5kW..
 
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Cliff C

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bear in mind that not all loads will be in use simultaneously. applying diversity, I'd allow for an aveage load of 8kW. that equates to c. 40A, so as far as current capacity, 16mm will,be fine. volt drop however may be a factor.
Thank you everyone for your advice.

The reason I put my post was that I had two conflicting quotes from local electricians.

One said that my existing 16mm armoured cable would be OK and quoted me £480 to upgrade my outdated fuse box with a new consumer unit including safety certificate.

The other said that 16mm would be unsafe and a fire risk and quoted me £6900 to replace with 25mm armoured cable.

Will my 16mm cable by unsafe and a fire risk, or just a voltage drop that will mean I might have to replace my existing fluorescent fittings?
 

Spoon

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Thank you everyone for your advice.

The reason I put my post was that I had two conflicting quotes from local electricians.

One said that my existing 16mm armoured cable would be OK and quoted me £480 to upgrade my outdated fuse box with a new consumer unit including safety certificate.

The other said that 16mm would be unsafe and a fire risk and quoted me £6900 to replace with 25mm armoured cable.

Will my 16mm cable by unsafe and a fire risk, or just a voltage drop that will mean I might have to replace my existing fluorescent fittings?
What size circuit breaker/fuse did the electricians quote, for this circuit?
 

Wilko

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Hi - 16mm SWA buried is good for 78A single phase, which is about 18kW load. Your loads add up to less than this so in my humble opinion it's not the 16mm that might be a fire hazard. (It might be something else he's spotted?). Certainly there would be a significant voltage drop over 100m.
 

Spoon

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The quote wasn't detailed and did not say.
Ok.
As mentioned above, if you want to use the existing 16mm cable then the max size breaker/fuse you can have is 25A. Anything bigger and you will exceed the 3% voltage drop for your lighting.
 

ChrisElectrical88

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If you are using the office for yourself and are concious on what you are using together then the 16mm on a 25A MCB should be ok. Must be a big shed for that many heaters?

I would go with the upgrade however and get a fully detailed quote before placing the order.
 

Strima

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I would be using a fuse at source otherwise it could be a long walk when something trips out.
 

UKPN

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I am not an electrician. Can any
You're obviously in possession of warm clothing.
I get 23.91 Amperes with just the heaters on full balls.
i could not be arsed to work out the VD as books are in van. however, for wtat it would cost to replace the 16mm cable versus exceeding the 3% for lighting, I'd fit LED lights which are happy with a slightly reduced voltage and sod it. at the end if the day, it's only a shed, not a hospital operating theatre. tin hat ready.
one help please?

I have an outbuilding which I am converting into two offices.

The building is currently served by a 16mm armoured cable running underground from my house, the distance is about 100 metres.

Potentially the building could have a maximum of the following appliances:-

2x2kw electric oil filled radiators
1x1.5kw electric oil filled radiator
Hand wash 2.5kw
Electric Kettle 2.5kw
Saniflo 400 watts
Vacuum Cleaner 1kw
4 Fluorescent Lights
2 Computers
Total aprox 13kw

Will the existing 16mm cable be adequate or will I have to have it replaced with a 25mm armoured cable.

Thank you
 

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