Supply to garage.

[Edward67]

Hi ok here we go.
Friend has asked if can rewire his garage as he is turning it into a gym. I said ok no problem.

He the put the spanner in. Ok I want
1 circuit for a car charger. 7.4kw.
2 x 3kw heaters
1 x ring main for gym equipment. From what i can tell running machine is most power hungry.
1 x lighting circuit.

All on a 2.5mm incoming swa.

So now I need to split the meter tails.in the cupboard and put in 25mm swa cable. Run about 12 meters.

Pme 80amp.

So looking for thoughts.

He needs cutout upgrading to 100amp. Its large 5 bed already with a hot tub.

Do you think I should install 2 core swa and TT the garage.

Or 3 core swa to mini board in meter cupboard then to isolator.
Or a two core swa with separate earth cable run next to it. This is better as earth can be smaller diameter.

Due to the size of the earthing conductor with the mini boards even accept them.

Or thinking outside the box. I could run the swa and terminate to a metal bracket mounted in the meter cupboard then run into a double isolator switch which will protect the current house tails and new swa tails.
The issue with this is the tails from the bracket to isolator are not double insulated.
However they are In cupboard that requires a key to enter so does that comply. I'm not sure.

I already know about the debated exporting pme conversation so don't wish to revisit it please.

Looking for ideas or pictures of people who have performed this.
If it wasn't for a friend I would refuse because sometimes it's best to DGI.

All comments appreciated.

Pic.of meter cupboard attached. Mmmm loads of space? think there is room for mini board.

 

[TJ Anderson]

TJ Anderson thanks for response. My response you highlighted doesn't read well. I will try to explain better for discussion. That's what it is discussion not criticism.
When meter tails are over 3m an isolator is normally needed to satisfy the dno.
If the tails were split with say swa cable and a neat way was found to terminate the swa without the need of a fused switch then what is the difference between the new swa tails and the existing house tails? If they the same rating?
The difference the swa is actually better protected than the original tails that run for 15 meters through the house.
The discussion was if the new tails absolutely have to have a fused switch then why is just an isolator acceptable for every other property in the uk with meter tails over 3m.
I will be using a fused switch, I will be changing cable size to xlpe because of its increased rating I will be TTing the system.
The reason for the TT is its safer.

I can speck the install 100 percent because he doesnt know how many chargers he wants in the future. Most probably 2 but not ruled out more.
I hold my hands up to not knowing the true capabilities of xlpe cable over standard swa but I have now been educated

Discussion forum not criticism forum. People come on for help and advice in improving installs not to be picked apart otherwise what's the point.

Thank you. I apologise for my outrageous behaviour.

Absolutely......Let's continue our discussion.....

I am pleased to hear about your revelation regarding XLPE SWA. Amazing stuff it is. Can you educate me as to the equipment you are now designing to run at 90 Degrees Celsius? I have never got to do that in my limited electrical dabblings as I struggled to find suitable reasonably priced items for garages and garden shed installs etc

Why is TT safer here, we only have that PME at work. Am I in danger, I really don't understand??
[automerge]1595116417[/automerge]

Thankyou now that is what I call a well constructured reply. Explains the point very clearly and explains my question.

Again, I'm terribly sorry and I'd like to add the irony of this was not lost on me.

 

[Edward67]

Thank you. I apologise for my outrageous behaviour.

Absolutely......Let's continue our discussion.....

I am pleased to hear to hear about your revelation regarding XLPE SWA. Can you educate me as to the equipment you are now designing to run at 90 Degrees Celsius? I have never got to do that in my limited electrical dabblings as I struggled to find suitable reasonably priced items for garages and garden shed installs etc

Why is TT safer here, we only have that PME earth thing at work. Am I in danger, I really don't understand??

A

Thank you. I apologise for my outrageous behaviour.

Absolutely......Let's continue our discussion.....

I am pleased to hear about your revelation regarding XLPE SWA. Amazing stuff it is. Can you educate me as to the equipment you are now designing to run at 90 Degrees Celsius? I have never got to do that in my limited electrical dabblings as I struggled to find suitable reasonably priced items for garages and garden shed installs etc

Why is TT safer here, we only have that PME at work. Am I in danger, I really don't understand??

Really helpful king of person. Thanks.
Two quotes. You don't know what you don't know.
And don't judge someone on their worst day to you on your best.

Now rather than criticising either help my understanding or go away. You hold the 2396 so you are perfectly capable of explaining.

I would try and explain my reasoning but sure you would just RIP it apart with no explanation.

I don't know your background and will not guess but I often find the best designers are the worst installers and the best installers are the worse designers.

Goodnight.

 

[richy3333]

For fear of this turning into a keyboard fight and getting moderated i would suggest to the OP (and am sorry if this upsets you as it is meant as positive criticism), but having read 2 pages of posts I do believe the job is beyond you; certainly from a design perspective at any rate.

Your original post details a very standard type of installation that we as sparkies often do, but your questions and comments do indicate it is something you have possibly not yet tackled before. Can you not get a more experienced contractor to let you shadow them and see how it’s done? Maybe someone from the forum can help?

 

[radiohead]

It has struck me over time on this forum that a simple supply to an outbuilding/garage/shed often seems to become a monumentally complex issue for no apparent reason.

 

[Edward67]

For fear of this turning into a keyboard fight and getting moderated i would suggest to the OP (and am sorry if this upsets you as it is meant as positive criticism), but having read 2 pages of posts I do believe the job is beyond you; certainly from a design perspective at any rate.

Your original post details a very standard type of installation that we as sparkies often do, but your questions and comments do indicate it is something you have possibly not yet tackled before. Can you not get a more experienced contractor to let you shadow them and see how it’s done? Maybe someone from the forum can help?

Was having bad day yesterday. Little.one went to hospital with peanut reaction so will take it o the chin.
Mr TJAnderson has opened my eyes to looking at it from a different perspective and he is entirely correct in his xlpe comment on cable selection.
I have got another very experienced contractor to aid in this but wanted to explore all options in open environment.
I think the forum would a better place if instead of people just saying why or wouldn't do that they explain their own view and reasoning as in with pme. Which has been discussed numerous times on many forums and always results in differing opinions.
Any more information on exporting pme that is concrete and not a personal view would be appreciated.

 

[7029 dave]

It has struck me over time on this forum that a simple supply to an outbuilding/garage/shed often seems to become a monumentally complex issue for no apparent reason.

Might have something to do with special locations

 

[pc1966]

Also it is not a "standard circuit" that you can just look in the OSG table for a yes/no based on load, length and CSA.

There is the special location side - the whole CPC from PME in another location with or without extraneous conductive parts bonding to worry about.

Then you have the simple circuit, say a couple of sockets and FCU for lights fed from house CU slot, versus a sub-main to a 2nd CU/DB and the whole OCPD/RCD selectivity arguments that go with planning that.

 

[richy3333]

@Edward67 hope the little dude is ok, really worrying when as a dad you can’t fix it and have to trust others.

The forum works best (imho) when someone says whom they are, their experience and then ask for help, having shown their calculations and described what they are to achieve or drawn a diagram etc. Part of the problem is that there are too many DIYers on here pretending to know something when they clearly don’t (I’m in no way suggesting that’s you).

I hope you keep posting questions ?

 

[Edward67]

@Edward67 hope the little dude is ok, really worrying when as a dad you can’t fix it and have to trust others.

The forum works best (imho) when someone says whom they are, their experience and then ask for help, having shown their calculations and described what they are to achieve or drawn a diagram etc. Part of the problem is that there are too many DIYers on here pretending to know something when they clearly don’t (I’m in no way suggesting that’s you).

I hope you keep posting questions ?

Ok will attempt to post with more depth in future.

 

[radiohead]

Any more information on exporting pme that is concrete and not a personal view would be appreciated.

You are not 'exporting PME', you are simply extending an existing earthing system.
I've never ever heard anyone say they are 'exporting TNS....or TT'.

Might have something to do with special locations

It's not a special location.

 

[DPG]

That's half the problem - the phrase 'exporting PME'. Can we just abolish it here and now??!!

 

[TJ Anderson]

You are not 'exporting PME', you are simply extending an existing earthing system.
I've never ever heard anyone say they are 'exporting TNS....or TT'.

It's not a special location.

The car charger comes under Special installations (722). That's what I was getting at when asking regarding why going for TT. He may be still ok with PME still if nothing is extraneous and also that the charger meets criteria of 722.411.4.1 (iii).

 

[radiohead]

The car charger comes under Special installations (722). That's what I was getting at when asking regarding why going for TT. He may be still ok with PME still if nothing is extraneous and also that the charger meets criteria of 722.411.4.1 (iii).

Yes absolutely right, when I posted I had in mind my general point about sheds/garages etc and completely forgot the OP's job includes a car charger.

 

[davesparks]

If the remote building has a concrete earth floor, or conductive floor, or the building is of metal construction or metal outside skin, the shock risk is increased. It’s therefore recommended that the remote building has a TT earthing system.

I've not seen anything in the regulations, or in the rules for the application of PME preventing its use in concrete floored buildings, not have I ever heard of a DNO refusing to provide a PME connection due to a building having a concrete floor.
Yes for some metal structures they will refuse to provide a PME connection due to the increased risk.

Do you have any reasonable evidence to explain and support this, regulations, guides to the regulations, technical publications etc?

When meter tails are over 3m an isolator is normally needed to satisfy the dno.

The discussion was if the new tails absolutely have to have a fused switch then why is just an isolator acceptable for every other property in the uk with meter tails over 3m.

The reason for the TT is its safer.

A fuse or circuit breaker is required to satisfy the DNO as they do not allow their fuse to be used to protect tails over 3m long (in most cases although some do allow 4m and some say the length must include the tails from cutout to meter)

Just an isolator is not acceptable for every other property in the UK with tails over 3m.

TT is not safer to the best of my knowledge, unless you can get a very good resistance to earth from the earth electrodes you install, then it may become equally safe.
PME provides a very low resistance earth directly back to the transformer, TT generally provides a much higher resistance path which can vary with seasonal changes and disturbance of the ground.
The last set of earth rods I installed had a combined Ra of 18 ohms, that's over 50 times the design value of a PME earthing connection for a 100A service.

 

[Edward67]

That's half the problem - the phrase 'exporting PME'. Can we just abolish it here and now??!!

How would you like to explain it so we can avoid the endless circle.

I've not seen anything in the regulations, or in the rules for the application of PME preventing its use in concrete floored buildings, not have I ever heard of a DNO refusing to provide a PME connection due to a building having a concrete floor.
Yes for some metal structures they will refuse to provide a PME connection due to the increased risk.

Do you have any reasonable evidence to explain and support this, regulations, guides to the regulations, technical publications etc?


A fuse or circuit breaker is required to satisfy the DNO as they do not allow their fuse to be used to protect tails over 3m long (in most cases although some do allow 4m and some say the length must include the tails from cutout to meter)

Just an isolator is not acceptable for every other property in the UK with tails over 3m.

TT is not safer to the best of my knowledge, unless you can get a very good resistance to earth from the earth electrodes you install, then it may become equally safe.
PME provides a very low resistance earth directly back to the transformer, TT generally provides a much higher resistance path which can vary with seasonal changes and disturbance of the ground.
The last set of earth rods I installed had a combined Ra of 18 ohms, that's over 50 times the design value of a PME earthing connection for a 100A service.

I was referring to an article in electri

I've not seen anything in the regulations, or in the rules for the application of PME preventing its use in concrete floored buildings, not have I ever heard of a DNO refusing to provide a PME connection due to a building having a concrete floor.
Yes for some metal structures they will refuse to provide a PME connection due to the increased risk.

Do you have any reasonable evidence to explain and support this, regulations, guides to the regulations, technical publications etc?


A fuse or circuit breaker is required to satisfy the DNO as they do not allow their fuse to be used to protect tails over 3m long (in most cases although some do allow 4m and some say the length must include the tails from cutout to meter)

Just an isolator is not acceptable for every other property in the UK with tails over 3m.

TT is not safer to the best of my knowledge, unless you can get a very good resistance to earth from the earth electrodes you install, then it may become equally safe.
PME provides a very low resistance earth directly back to the transformer, TT generally provides a much higher resistance path which can vary with seasonal changes and disturbance of the ground.
The last set of earth rods I installed had a combined Ra of 18 ohms, that's over 50 times the design value of a PME earthing connection for a 100A service.

Exporting A PME Supply To Another Building

In this article the technical team at Stroma Certification offers expert guidance on exporting a PME supply to another building. One of the most common queries to the Stroma help desk concerns running

professional-electrician.com

Doesn't say it's not allowed but was referring back to this.

 

[davesparks]

I was referring to an article in electri

Exporting A PME Supply To Another Building

In this article the technical team at Stroma Certification offers expert guidance on exporting a PME supply to another building. One of the most common queries to the Stroma help desk concerns running

professional-electrician.com

Doesn't say it's not allowed but was referring back to this.

Ah yes, that well known source of verified technical information, the freebie mag from the wholesalers.

The article makes some good points but also makes some mistakes.
There is nothing, as far as I am aware, preventing the use of an earth from a PME supply being used in a building with a concrete floor.
I'm sure a lot of us have been to, and worked on, installations which have a PME supply and a concrete floor.

 

[radiohead]

I'm sure a lot of us have been to, and worked on, installations which have a PME supply and a concrete floor.

Probably a majority of buildings with a PME supply have a concrete floor.
My house does. And so does my attached garage, it's on the same PME as the house.
I do often wonder why the 'exporting' thing only seems to apply to PME??
Why dont we 'export' TT or TNS?
And why does it only apply to outbuildings? Why does the fear of PME seem only to apply to outbuildings?
I 'exported' the PME to a socket by a pond last week, never ever seen anyone TT a pond socket..

 

[davesparks]

I 'exported' the PME to a socket by a pond last week, never ever seen anyone TT a pond socket..

I'd keep quiet about that if I were you, otherwise someone will be along with an eath rod and drive it straight through your pond lining!

All that water leaking down the earth rod will be great for keeping the Ra down, but pretty terminal for the prize koi!

 

[TJ Anderson]

Probably a majority of buildings with a PME supply have a concrete floor.
My house does. And so does my attached garage, it's on the same PME as the house.
I do often wonder why the 'exporting' thing only seems to apply to PME??
Why dont we 'export' TT or TNS?
And why does it only apply to outbuildings? Why does the fear of PME seem only to apply to outbuildings?
I 'exported' the PME to a socket by a pond last week, never ever seen anyone TT a pond socket..

It only applies to PME because of the of the potential risk of exposed and extraneous conductive parts rising to mains potential if the PEN conductor suffered a broken earthed neutral and the line conductor stayed intact. This cannot occur on a TN-S or a TT as they have separate conductors.

 

[radiohead]

It only applies to PME because of the of the potential risk of exposed and extraneous conductive parts rising to mains potential if the PEN conductor suffered a broken earthed neutral and the line conductor stayed intact. This cannot occur on a TN-S or a TT as they have separate conductors.

I understand the potential dangers of PME supplies, I don't need that explaining.
But it does not explain why only PME is apparently 'exported', TNS and TT are also 'exported' where they feed a remote installation .
Neither does it explain why PME is only ever 'exported' to outbuildings. There are many other situations remote from the intake where 'exported' PME is never questioned. The pond socket I installed last week. External lighting/garden lighting. I recall a job a few years back where the installer had fed a string of drive light columns from the TNCS house supply, and run a distribution circuit to a summer house which had been separated and TT'd......so they couldn't export the PME to the shed but it was fine on the drive lights!
I just hate the term 'exported' and the lack of logic behind only applying it to outbuildings.

 

[TJ Anderson]

They only mean extending the earth outsider by the term exporting so I am not worried about the terminology. They could be more specific regarding outbuildings (as with Caravans) but it is really because the impact of a PEN failure is likely to be more severe with some outbuildings dependant on what is being supplied in them. Lots of class 1 metal cased equipment for example and also just having exposed ground or concrete. Also what is the likelyhood of someone being in contact with it. The way it is at the moment allows an electrician to apply his/her judgement and I prefer that.

My home has PME. My garage is remote from my house and I utilise the distribution circuit earth. I don’t have lots of metal cased class 1 equipment. If I did, I might consider changing it to TT.

Your pond pump (likely class 2) would not be any risk at all even under an PEN failure conditions.