Wiring up external garage

[apdevelopments]

I am having alittle trouble trying to get to grips with putting power to my garage which is next to my house.

I already have power to my garage via a 60ft length of 2.5 armored cable.

The run starts from the consumer unit in the house and is protected with a 30ma RCBO.

But I would like to fit a new consumer unit to my garage and bring it up to 17th edition.

I would like to use this job for my first assessment with elecsa. Yes Im a newbie to all of this and I am still at college. :innocent My garage will have different circuits including a ring as I want to build it into a wood workshop.

Anyway. First of all I know that I need to change the RCBO in the consumer unit for a time delayed unit as I will have another RCD in the garage.

I also know that I am aloud up to 3% voltage drop in the length of cable as I will be fitting a lighting circuit. No problems here as there is only 1volt drop according to my meter readings.

The big question is DO I NEED A EARTH ROD rammed into the ground next to my garage and take away the earth run in the armored cable. Making the garage into a TT system?

What is the max length of armored cable aloud before I need a earth rod? as I can shorten the armored cable run to 48ft by re routing it.

Any help would be great as i dont want to sound a plant pot.

Many thanks

 

[Badger]

60ft of 2.5mm what voltage are you getting at the end of it 100 volts!! if thats the length of run that id have installed then id have thought more 6mm to bo henost.

 

[apdevelopments]

Hi.

Voltage at the source is 245 volts and voltage at the garage is 244 volts.

 

[Manator]

First question is what is the present earthing arrangement, as this would have a bearing on if a rod is needed or not. Next you say you want to turn the garage into a wood shop, the calculations need to be made as to the demand, this will then determine what protective devise you will need to use and the length and volt drop verification will tell you what size cable to use.

 

[revjames]

Hi.Voltage at the source is 245 volts and voltage at the garage is 244 volts.

Whats the voltage when you are using an arc welder or when its cold and you have a 3kw heater on?

 

[Doc Hudson]

Hi.Voltage at the source is 245 volts and voltage at the garage is 244 volts.

Welcome to the forum apdevelopments, To be quite open and honest I am very concerned at the level of your questioning, you do indeed have a few difficulties. This is not how you calculate voltdrop. Remember the supply company is allowed to let their supply voltage fluctuate by a set percentage. It would have been just as possible to get a higher reading at the end of you cable depending upon the network loadings at the time when you did your reading. Volt drop is calculated based on the current demand along the circuit, the length and the tables of mv/a/m from BS7671. Have you ever done these calculations at college? As Manator asked the earthing arrangements at the main house needs to be known. The question of if a rod is used or not is not governed by the length of the SWA. And as Badger pointed out 2.5mm sounds very small C.S.A. for what you are planning.

I would suggest you either; Wait until you finish college and have passed you exams before taking this project any further Or get a qualified electrician to work along side you and teach you some practical and theoretical skills as you do the project together. Then once you have this working exercise under you belt, try using a new project as your assessment. Many of our members would suggest you are asking quite basic questions and you should have a better grasp by now if trying to use the project as an assessment.

Doc H.

 

[kme]

I am having alittle trouble trying to get to grips with putting power to my garage which is next to my house.I already have power to my garage via a 60ft length of 2.5 armored cable.

The run starts from the consumer unit in the house and is protected with a 30ma RCBO.

OK - its looking good so far; though you haven`t told us the rating of the RCBo; and, as has been pointed out above, a voltage drop develops under load ( think of ohms law?)

But I would like to fit a new consumer unit to my garage and bring it up to 17th edition.

OK - not an issue. Why do you think it isn`t compliant with 7671(17th ed.) currently?

I would like to use this job for my first assessment with elecsa. Yes Im a newbie to all of this and I am still at college. :innocent My garage will have different circuits including a ring as I want to build it into a wood workshop.

Now. depending on the size of "workshop", and no./ type/ loading of machines, will determine many other things, including cable size, no & type of circuit, final cct cable sizes, etc. Again, not enough info.

Anyway. First of all I know that I need to change the RCBO in the consumer unit for a time delayed unit as I will have another RCD in the garage.

Why? You might change your mind when you find out the cost (and possible unavailability) of a time-delayed RCBo that is compatible with your DB.

I also know that I am allowed up to 3% voltage drop in the length of cable as I will be fitting a lighting circuit. No problems here as there is only 1volt drop according to my meter readings.

I would assume you have NOT taken this measurement under load? ; in which case its meaningless.

The big question is DO I NEED A EARTH ROD rammed into the ground next to my garage and take away the earth run in the armored cable. Making the garage into a TT system?

Depends on circumstances. What is your current earthing system; what is Ib, In and Iz for the sub-main; what is the construction and service supply situation to the garage? Will the armour be sufficient as the earth when the adiabatic is applied?

What is the max length of armored cable allowed before I need a earth rod?

EH??? Where did you get the idea that there is any correlation between the two?

as I can shorten the armored cable run to 48ft by re routing it.Any help would be great as i dont want to sound a plant pot.

Many thanks

I would suggest a bit of research in your books to be advantageous mate; as you haven`t provided many of the salient points, and seem to have a few misunderstandings of the theoretical design stage. Can I suggest doing a bit of reading of the OSG & BRB; searching a few old threads on garage supplies, then give us another post? Thanks, and welcome to the forum.

n.b. "plant pot"? Maybe it`d be worth keeping a couple handy......... :tongue in cheek

KME

 

[apdevelopments]

Hi again.

I didn't install the cable it was here when I first moved here. I did wonder if its big enough.

There is a single 13amp plug and a single 100w light bulb so it was probably ok

But when I put what I want to run into the situation with my new layout I think I will need a bigger cable.

The garage is supplied a B20 RCBO in the consumer unit.

I did try your load voltage test and Normal static voltage was 243 volts and with a 2KW load from a Fan Heater the voltage dropped to 237 volts so I would guess with a bigger load of 3kw the voltage would exceed the 3% that your aloud in the regs.

So for my new workshop setup I would like. 1 Lighting circuit two fluorescent tubes. with a strapper putting a light switch at each end of the garage. A ring main with at least 6 double sockets around the garage. This is to power my saws, lathes and pillar drills. ((All domestic plugs on equipment ))) A separate 16amp socket for my wifes GWiz car charging. The electric car charging requires 8 amps over night.

What size cable would you use??

What about that earth rod???

Ps ive just passed my 17 edition. 2382-10 and currently working on the 2392-10 inspection and test. :innocent

Oh Yes she has a Gwiz!!!!!!! :slap

 

[ktguk]

this might help

http://www.napitonline.com/downloads/CP%205%2007%2016th%20P%208-9%20Supply%20to%20Detached%20Outbuilding.pdf

 

[Apache]

Ok calculate your maximum demand. If all your wood working machinery supplied by a 13A plug and you are the only person using the equipment then 13A + 1A [lighting] + 8A car charging [you gonna put a heater out there for winter - oil filled radiator adds 11A, a dust extractor could add another five amps to your 13A table saw etc etc]

The we know the distance and can start to calc cable size.

 

[Andy™]

So for my new workshop setup I would like. 1 Lighting circuit two fluorescent tubes. with a strapper putting a light switch at each end of the garage. A ring main with at least 6 double sockets around the garage. This is to power my saws, lathes and pillar drills. ((All domestic plugs on equipment ))) A separate 16amp socket for my wifes GWiz car charging. The electric car charging requires 8 amps over night.

if the submain is only 20A, how do you plan on installing a 32A ring main?

for someone who is using this job as an assessment, you seem to have a serious lack of knowledge. and by the way you work out VD using a multimeter, id say your chances of passing said assessment is about the ame as me winning the lottery on friday.

and if your asking questions like this, i doubt your going to get far with 2392

if i was you, i would cancel the assessment, 2392 & this projeact until you know more. well, maybe plan it, but thats about it

 

[apdevelopments]

A friend of mine recommends using 10mm armored cable for this distance and the earth in cable will be sufficient.

Replacing the B20 RCBO in the house consumer unit to a higher rated RCBO ie B40 or B50 30ma RCBO with a time delay.

What you thinks? is he on the mark?

 

[matt.leung]

how is the cable run, clipped direct to a fence or wall, buried in the ground ???

 

[Sidewinder]

ap,

You really need to start at the end mate.

You need to know what loading you are expecting then add a margin for future expansion.

Once you have that you can look at the layout etc. in the workshop to be.

From there you work backwards, but there is a lot more to this than just stuffing in a bigger breaker at the source end.

 

[Manator]

apdevelopments, this forum works on the basis that if you ask a question the members will point you in the direction you need to be looking, you then must go and do some working out, then post back what you have worked out so that the members can show you were you are going wrong, or what your doing right. If some member gives you the direct answer, you will learn nothing, and when you do get assessed the assessor will know this.

Do not be bashful with your replies, it all helps in the learning process, because it is only when you understand how a circuit is designed, that you can really truly install it.

 

[NozSpark]

Have you actually done any cable calculations or are you just guessing??

It's not exactly difficult..

Volt drop, along with current carrying, capacity is in the tables in the back of the BRB and is expressed in mV/A/m

 

[Apache]

What you thinks? is he on the mark?

I think you should listen to some advice you have been given.

We don't give a damn what size your mate thinks you need. What happens when you work for a customer and they want a supply to a shed - ring your mate and ask him.

You're a student and you are learning. You should know the process of how to work this out. If you don't know then I really worry about you holding some of the qualifications that you say you do.

You should be keen to know WHY you need a certain cable size, WHY you may need to TT the building WHAT the maximum demand is likely to be.

Once you have worked out max demand, volt drop calcs and whether your existing CU can handle the extra load [50A - really?] then come back to us. Hopefully a mod will move this into the student and learning section because there's a lot of learning to be done. I'm not a spark and I know this and could work out the numbers.

 

[Manator]

I have moved this to the student area, I feel the advise will be more helpful if the level of questions are as basic as this, and it will help everyone if used as a practical example.

On a side note I remember a similar type of example being used as a training aid.

 

[steptoe]

Ok calculate your maximum demand. If all your wood working machinery supplied by a 13A plug and you are the only person using the equipment then 13A + 1A [lighting] + 8A car charging [you gonna put a heater out there for winter - oil filled radiator adds 11A, a dust extractor could add another five amps to your 13A table saw etc etc]The we know the distance and can start to calc cable size.

I would perhaps double up on the machinery,

a lathe could be running on freefall, so to speak,

or if he is really posh a CNC miller or such like,

oh, and the 1A lighting, what about the 2 500w halogens he will fit come october, and the high intensity lamps for the detail turning work,,,,,,,,

but you have certainly made a very good starting point,

 

[Apache]

On a side note I remember a similar type of example being used as a training aid.

You think we're doing this lad's homework?