I just had a quick look and amendment 2 BS7671 section 443 now says
Protection against transient overvoltages shall be provided where the consequence caused by over voltage could result in:
i. Serious injury or loss of human life
ii. Significant financial or data loss”
But surely those consequences could result almost anywhere where there’s main voltage in the UK depending on how the equipment was being used.
Surges are not just lightning strikes and can be caused on the network due to faulty plant. When living in South Australia surges were common as the generating system was under stress, brownouts were common occurance and on return from temporary interruptions there can be momentary surges. It is rare in the UK to get a surge which causes damage but it can happen.
Certainly a consideration, and I think it can be more of an issue in rural areas. I recall about 25 years ago the houses in my road getting a. search, and Norweb people were around in the street finding out what had broke, and then offering a replacement/repair. From what I recall it was just a few house alarms that required fixing, and it was pre-Naim for me. So I’m happy to take that risk, on the basis I think its low - I could be proved wrong of course
Hm - interesting one. Of course how do you define significant - after all it’s not a Statement. I might argue that the new radial line is no worse than it was before hand, or arguably better as I am now using an RCBO, rather than a 25 year old RCD. May loose that argument though. Still happy to take that risk
Which is why Surge protection devices are now in the requirement.
Suggest having a look at the RS web-site on surge protection - should be easy to find.
As above, my understanding is that SP is being advocated on a risk-assessed basis (and isn’t mandatory) due to the increase in sensitive electrical kit in homes (and in wider use industrially, especially IT/computing/telecoms), this driven by potential mains surges post brown-outs and other disturbances to Grid supply (lightning must be excluded here given other entry points in to a home).
The UK Grid is relatively stable (notional 230v) but some generators/providers are obviously concerned about supply risks and, looking forward, one can understand why.
As @GadgetMan says, until there is assurance these protections won’t adversely affect sound quality (removing some of the benefits of your new CU!), it’s my view it’s not a matter for concern/action - further noting so many legacy installations would be non-compliant to 18th regs in any event (but are still OK). Obviously, YMMV.
Actually, exactly like a wind tunnel as they suck rather than blow in order to ensure smooth laminar airflow…
That makes sense.
No. The size 10mm2 refers to the cross-sectional diameter of the cores so the overall diameter is 21.8mm .
It’s quite a big cable.
This gives a comparison between the different sizes.
DG…
Yes, thanks - that was also answered above.
In my ignorance when I first got into Naim boxes and before joining the Forum, the advice via the dealer from another customer who was an electrician was to use 4mm CY screen earthed at the CU end. I didn’t put in separate CU. The system still gives me lots of Wows!
Now with a Air Source Heat Pump I get transformer hum when the ASHP is running, As we have Solar & Battery coming at the end of January and an EV around Christmas we need more circuits as the small box for the Oven and hob, utility room and an upstairs radial for second HiFi is full and the main CU has a further 13 circuits! So it a 6 way for the inverters (ASHP, Tumble Drier in utility, Solar, Battery, EV charger and an energy monitor for the ASHP so I know how much juice it uses) and a 2 way for the hifi. The electrician said they could put in a really long Earth rod to the hifi. We already have the 3 way Henley blocks.
Very difficult getting the electrician to come and do it though.
Phil
If your house gets its earth from its incoming Mains, then I don’t think an electrician will be allowed to have a circuit with earth coming from a rod. I don’t believe these can be mixed in a building. It’s either all through a rod, or all from the mains
I called out Western Power Distribution a few years ago because we have PME and an earth rod. They said it was alright.
What the electrician will do is up to him. The current earth rod is right next to the foundations and may suffer in dry weather although it has a concrete path over it to stabilise moisture. Another property off the same pole is not on PME when it was converted 20 years later! I don’t mind not having PME.
Phil
I see, if the house is already connected to a rod, that makes sense. I don’t know much about rod installations, but I understand that some have to be watered every now and then in dry conditions
What is the case for 16A MCB v 32A?
Do the regs require the cable being protected to be rated above the MCB?
If the boxes don’t trip when powered up is there any difference in SQ?
Phil
No reason why you couldn’t use 16A, but I would imagine/guess that the connections inside the MCB are larger.
Do you mean 4mm ‘SY’ twin & earth cable?
Did you adopt this method and if so can you remember how exactly the braid screen was earthed at the CU?
I take this was some time ago so probably not a metal box CU with a gland connection (?)
It is a metal CU and the cable is earthed at the CU end. I thought it was CY. It has a clear outer insulator with the braided screen below etc. The conductors and earth are all 4mm2. The cable has a circular cross section. The three cables are insulated in the normal way and probably encased in another insulator then the screen.
Perversely the CU is a metal Square D from 1989!
Phil
Yes the N L & E wires are connected in the normal way and using an MCB fuse such as a 32A.
Usually the braided screen is unravelled a few inches from the end of the cable, then twirled into a couple of tufts which are then secured onto a brass gland clamped onto the metalwork of the CU.
I have a new run of 6mm SY cable ready and waiting to plumb in, but need to figure out how the braid maybe earthed into a plastic CU (MK Sentry 2014).
Don’t really feel the need to update the CU after only 8 years.
The usual way to earth the metal braiding in a cable is to connect it to a spare slot in the earthing bar. A ‘banjo’ washer is used on the gland as it has a lug on it which allows a short length of earth cable to be fitted inside the box. This would be the same on either a plastic or metal CU.
(On a metal consumer unit I’ve seen attempts to connect the braid directly to the metal box as this, in turn, will be connected to the same earth, but this is bad practice as it doesn’t guarantee a good electrical connection.)
I say this with the usual caveat that I’m not a qualified electrician. I’m sure yours will be able to do all this correctly when they install it.
