Help with Marinas

[Doomed]

I have been testing the shore side cabinets around a harbourside and the pontoons onto witch people moor thier boats, there are electrical outlet pillers on these pontoons fed from the harbour edge cabinets.
All well and good, apart from the supply to the pontoons.
About 2 thirds are TT supplied using SWA and the other third is TNS using SWA, although the origen of the TNS cabinet is a SWA feed from a main switch room supplied by a TNC-S DNO supply.
My question is why the difference.
The BRB says no TNC-S to any boats, but does this mean that the TNS supplies are a no no, or does it just mean no TNC-S, and if it does not why are there so many TT supplies around the harbour?
Out of curiosity I tested the Zs reading in a cabinet using the disconnected TNS earthing and compared it with the Ze reading from the TT in the cabinet and the TNS readings were much better.
Please someone give me some guidance about what to put on the test results etc.
Thank you.

 

[gnselectricals]

Only TT & TNS to marinas is ok just no TNCS due to the risks associated with loss of supply neutral as with caravan installs
Re the testing you just have to be methodical, iv tested a couple recently and have found it good to produce a simple schematic to aid you
Perhaps it would be beneficial to have a TNS Supply to the whole installation to aid with disconnection times, however there should be RCD protection to all the boatyard & pontoon moorings
These are pretty specialised areas that require a good understanding of the regs, can't offer much more advise as in Mexico at the mo & neglected to bring my BRB hut hope I've helped in some way
Regards gram

Sent from my iPhone using Tapatalk

 

[pushrod]

Ze on an a tn-s should be <0.8Ω . On a TT the Ze could be up to 200Ω - so any Zs on a tn-s would almost certainly be lower than the Ra / Ze readings on a TT - if i understand correctly what you were asking.

There will be lots of rcds to test as each individual socket should have its own rcd.

 

[Doomed]

so the main DNO TNC-S feed to the main switch room 200 yards inland is OK without converting to TT at the shore side cabinets? From the main switch room all the cabinets are supplied in SWA.

 

[johnboy6083]

all of the cabinets that you say are TNS, are actually fed from a TNC-S supply. This means that they must be converted to a TT system. If the supply transfromer is close to the switchroom, then it may be cheaper to ask for a TNS supply to be installed, than to go around, installing numerous rods, and associated RCD's.
Dont keep the TNC-s, as in the event of supply problem, you will end up with a lot of problems.
being near to the saea, if you go down the TT route, then you should get reasonably good readings, due to the salt content, and the moisture in the ground

 

[Electro-tech]

I would say that TNCS/ Main switchroom is fine. There are many houses with TNCS and the no no..no comes when you are exporting TNCS to a Garden or Shed,then you would TT it. The risk is a break in the PEN conductor. So TT would be no problem.

 

[Doomed]

Ah.
I was afraid of this.
This means that alot of the shore side cabinets will need converting to TT due to my inspection.
Unfortunately this is going to cause me no end of hassle.
There are two or three contactors who are always trying to win our local councils work.
The company I now work for has managed to get the contract to inspect all of the harbour cabinets, this work is normally split between all the contractors.
So whats the problem you ask, you have found faults which the other companies didn't which makes your employer look good.
Alas no.
I'm the new boy (middle aged bloke) with my firm, and all the faults are with the cabinets that my company has been inspecting for the last few years.
So I'm going to end up making my new employer look bad in the eyes of the local council.
Great way to start off a new job

 

[Guest123]

Some IET info here.....

 

[johnboy6083]

Ah.
I was afraid of this.
This means that alot of the shore side cabinets will need converting to TT due to my inspection.
Unfortunately this is going to cause me no end of hassle.
There are two or three contactors who are always trying to win our local councils work.
The company I now work for has managed to get the contract to inspect all of the harbour cabinets, this work is normally split between all the contractors.
So whats the problem you ask, you have found faults which the other companies didn't which makes your employer look good.
Alas no.
I'm the new boy (middle aged bloke) with my firm, and all the faults are with the cabinets that my company has been inspecting for the last few years.
So I'm going to end up making my new employer look bad in the eyes of the local council.
Great way to start off a new job

i understand only too well the problems your having. all you can do mate, is highlight the problems your seeing, and your knowledge and experience, and back this up with BS7671. dont mention how wrong the other people were, this will be self explanatory.

I take it that you photocopy your paperwork, before the boss gets to see it? this is something i do, because ive heard of employers, altering certificates in the past, to save face or money. At least if there are any comebacks, i can clear my name.

 

[Guest123]

Ah.
I was afraid of this.
This means that alot of the shore side cabinets will need converting to TT due to my inspection.
Unfortunately this is going to cause me no end of hassle.
There are two or three contactors who are always trying to win our local councils work.
The company I now work for has managed to get the contract to inspect all of the harbour cabinets, this work is normally split between all the contractors.
So whats the problem you ask, you have found faults which the other companies didn't which makes your employer look good.
Alas no.
I'm the new boy (middle aged bloke) with my firm, and all the faults are with the cabinets that my company has been inspecting for the last few years.
So I'm going to end up making my new employer look bad in the eyes of the local council.
Great way to start off a new job

Well TBH I'd rather be on the Nat King Cole knowing what I do is 100% correct rather than folding up and 'conforming' to keep the boss and the fat cats at the council happy.

Stick to your guns mate, report what you find with references to any applicable regs etc and at least your conscience will be clear.

 

[truckster]

Could you put a stake in at the supply end, disconnect all the TN-S supplies and put them all on one TT system? Seems an easier soution

 

[johnboy6083]

Could you put a stake in at the supply end, disconnect all the TN-S supplies and put them all on one TT system? Seems an easier soution

i wouldnt rely on one rod in this situation. Personally, i would install a few, and link them together. I would try and ensure that they were long enough to penetrate the water table, so that your readings are very stable.

 

[Doomed]

Know anyone who does 15' earth spikes
Seriously, thanks for all your help.