Tt overhead cables and surge protection.

[5544]

Can someone clarify something for me which to be honest I should know.

exporting power to a new outhouse and have noted that the house is TT, on insulated overhead cables.

this is the first time in ages I will have worked on TT, but noted that the system is old, and currently have no surge protection on the incoming supply.

user the current regs, is there a need for me to install surge protection since the cables are insulated.

Everything else I need to do is standard work.

The house is a detached house in the country.

 

[yellowvanman]

You need to make a risk assessment associated with what could get damaged by a surge and the likelihood of it happening. Theres nothing in the regs that say you must have surge protection,.

If the overheads are insulated maybe its been re-done recently, in which case maybe ask DNO to check if you can have PME!

 

[Colin Jenkins]

Hello 5544.

There's no need for surge protection.

Regards,

Colin Jenkins.

 

[Marvo]

When you say surge protection are you trying to protect IT equipment like computers from supply transients? I doubt surge protection will be effective on the high impedance TT systems allowable with up-front RCD under the UK regs. If your Ra is >25ohms and there's no pme available I'd save your money and not install it to be honest. *runs for cover*

 

[soulman]

As above, no need for surge protection.

 

[Engineer54]

Go and check the overhead poles yourself, if the system has been PME'd, then you should see the N-E earth rod cables at every 3rd or 4th pole. Generally accompanied by a metal or traffo PME warning notice fixed to the pole!!

 

[Knobhead]

LV OH cable is always insulated where it terminates at the house. It’s been a requirement since the early editions of the regulations.

Very early cable (1900’s) was insulated with two layers of impregnated paper covered in red lead soaked jute with a cotton overlay. (No I’m not that bloody old! Before any of you start on me.)

As for surge protection of IT equipment, if the phone line is overhead then that can be protected. I got fed up with my answer phone and modem blowing up, I fitted three Transorbs to the incoming line. They had a strike over voltage of 250V, could be pure chance but my phones kept working for years after.*

The mains, you can fit SP but it’s not a requirement. But bear in mind to be any good they have to handle the full fault current and they will be destroyed by a strike. The CU won’t fair much better. The ones I’ve seen I wouldn’t trust as far as I could throw them.

*I lived in the middle of nowhere at 1100’ elevation. Lightening was a fact of life, it’s going to happen at some time. Keep paying the insurance!

 

[alanl]

Hmm, there are some sweeping statements in the above posts.

Firstly, discard lightning protection, as it is beyond the scope of most people here, and is generally not economic for a domestic installation.
Unless you have seen, and assessed the installation, you cannot see if there is a definite need or not for surge protection.
In the main, Surge protection is recommended for overhead TT supplies as they are the type of supply most prone to voltage surges. These are not always big 'flash bang' surges, but 300Volts for less than a second.
The majority of appliances can handle these type of very short surges, but there are some items that could be damaged. I was asked to fit a SPD last year due to 2 TVs being damaged by surges.
Surge protection devices are not 'one-shot' devices, they are similar to self-setting circuit breakers, where they work if there is a surge, then reset once the fault has cleared. The duration of the surge can be so small that the user does not even know the device has worked.
This is why it is important to know the installation, and relevant history. If there have been surges before, then it is likely there will be more, unless the DNO has improved their network.
NICEIC, and Dehn both do one day courses in Surge Protection, and I'd recommend anyone to go on one of these.