Cable size

[uksparks]

Hi,

I am going to be connecting an out door power supply, away from the building, its all metal casing.

The supply is 10mm, I am using a 3 core SWA for part of the run, the inside part was going to be in twin and earth, but then I was just thinking, going on table 54.8 section 544.1, am I looking into this too much or does it need to have a 10mm earth as its extraneous metal which is fixed into the ground?

In which case I was just thinking of running 3x 10mm inside the building so the earth is 10mm too to them comply with min size of bonding conductor.

I am right to make it 10mm throughout the entire run aren't i?

 

[davesparks]

Well I called the NICEIC today and they said do not put an earth rod in and just take the SWA out the building and make it part of the TN-C-S installation.

I explained everything in full and explained the proximity to the building etc and that the building it metal and so on.

They even emailed me to confirm as I asked them, they said its fine, they said that in reality its never ever going to be a problem.

So, will the judge accept 'the NIC said it's ok' in preference to 'I followed bs7671 to the letter' ?

 

[ImpededLoop]

and also the fact that its a steel building with the steel bonded, he said thats more than likely better than any rod you will put in.

For once it sounds like a common sense outcome.

 

[spark 68]

so would it not be easier to use 3 core swa, amour earthed at db but not at evcp and use a tt system for the charging point than trying to meet 722.411.4.1 (i) or (ii) or (iii)

The problem here was the proximity of the PME bonded metal clad building to the TTd ECV, you would be able to touch both Earthing systems simultaneously, which is a shock hazard due to true Earth of the TT part relative to the PME part which may not be at true earth potential at any given time.

 

[davesparks]

They said the three phase part for section (i) and also the fact that its a steel building with the steel bonded, he said thats more than likely better than any rod you will put in.

More than likely better? That's a very precise and technical response!

Once you've tested the effectiveness of the steel structure as an earth then you will be better informed about this. Then with test results to prove it you could make the informed decision that this is safe to do.

 

[uksparks]

More than likely better? That's a very precise and technical response!

Once you've tested the effectiveness of the steel structure as an earth then you will be better informed about this. Then with test results to prove it you could make the informed decision that this is safe to do.

What would the best bethod be to achieve this on this type of buliding?

 

[spark 68]

First off I would be looking at the formula in the annexe associated with exemption i), then clamping the individual tails to see how balanced the building actually is when it is normally loaded, and adding up any further loads from the DB to see if it is possible to severely unbalance it, this would be my starting point.

I hinted at this last night when I said "Archies suggestion is looking better by the minute"

 

[davesparks]

First off I would be looking at the formula in the annexe associated with exemption i), then clamping the individual tails to see how balanced the building actually is when it is normally loaded, and adding up any further loads from the DB to see if it is possible to severely unbalance it, this would be my starting point.

I hinted at this last night when I said "Archies suggestion is looking better by the minute"

He's adding a 60A single phase load to the system, so unless the system is 60A out of balance then the system will be thrown out of balance when the charger is in use.

Clamping it will only give a brief snapshot of the loading, a couple of weeks load study would really be needed to establish a proper idea of what the loading is like.

 

[spark 68]

He's adding a 60A single phase load to the system, so unless the system is 60A out of balance then the system will be thrown out of balance when the charger is in use.

Clamping it will only give a brief snapshot of the loading, a couple of weeks load study would really be needed to establish a proper idea of what the loading is like.

I thought he was fitting a 3 phase charger ?

Agree that longer term monitoring would be a better bet, but if it is outside of the parameters of exemption I) to begin with then he is going to have to load balance it better to start with no?

 

[Simlec]

More to the point has anyone got an electric car to need the charger?
by the time you get it working we will all be in spaceships :driving::driving::driving:

 

[uksparks]

Yes they have two cars already that both draw 16A so that's 32A straight off.

I think without looking at my notes it was 8A on L1, about 30A on L2 and 8A on L3

I am going to put this on L1.

Im not being funny but nobody is ever going to monitor this for even a day let alone two weeks.

 

[uksparks]

I thought he was fitting a 3 phase charger ?

Agree that longer term monitoring would be a better bet, but if it is outside of the parameters of exemption I) to begin with then he is going to have to load balance it better to start with no?

I was toying with the idea but it was a non starter after discussing it with the manufacturer due to various reasons with the charge point.

 

[ImpededLoop]

Im not being funny but nobody is ever going to monitor this for even a day let alone two weeks.

You don't have to sit there logging it in person, a data logger does that for you and you download the data to your pc.

 

[uksparks]

First off I would be looking at the formula in the annexe associated with exemption i), then clamping the individual tails to see how balanced the building actually is when it is normally loaded, and adding up any further loads from the DB to see if it is possible to severely unbalance it, this would be my starting point.

I hinted at this last night when I said "Archies suggestion is looking better by the minute"

Ok but how would you actually test the steel structure, it will not be possibles to guarantee that the water service is 100% disconnected and you are only testing steel as probably cannot access every single part.
what would you do? Disconnect the main earth and try doing a Ze to the steel bond?

 

[spark 68]

My main point still stands, look closely at the formula in the associated annexe to exemption I) to see if you can get within the paramaters, you may have to juggle the loading about a bit, this is a starting point

 

[uksparks]

You don't have to sit there logging it in person, a data logger does that for you and you download the data to your pc.

I appreciate that, but it seems like we are all going a bit over the top, this is just a car charger thats being installed, it's no more than a glorified weatherproof socket on the side of the building.