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To say they are unsafe if in good condition is not quite right, they met the wiring regulations of many years ago.

But they are far less safe than a new CU would be for a couple of reasons and upgrading both is probably the single best thing you can do since a new CU offers:
  • RCD protection - a major reduction in shock risk (and to a smaller degree fire).
  • MCB trip on a lower overload and let through a lot less fault energy (at least up to the 1kA or so fault current) than fuses.
  • MCB can be reset easily by an unskilled (electrically speaking) person, and no risk of wrong fuse wire being used.
  • MCB can be used to isolate/restore a circuit without powering everything off (never ever change a rewirable fuse with the power on!).
  • It is also going to result in you house wiring being inspected/tested (done properly), either as an EICR before the CU change or as part of the deal. That can find faults that are not noticed in normal (no-fault) operations.
Also if you need any new circuits having a CU with spare slots allows better separation so faults are contained to less impact.


The reason for the wiring regulations having a maximum voltage drop of 3% on lighting circuits (compared to 5% on other) is to reduce the impact of load changes on the voltage, and resulting change in brightness.

Old filament lights are very sensitive to voltage, so a few percent has a noticeable effect, hence this concern. However LED lights have nowhere near the same change in brightness with voltage so they probably don't need the 3% rule.

But the regulations as they stand still say 3% for lights, and still advise on assuming 100W per light fitting when computing power use!


Some folk might think "arming yourself" sounds like it is a showdown with the electrician as many have had problems before with customers who think they know a lot more than they really do. But if you treat some of this discussion as points to go over with the sparky for ideas on how some of the issues could be solved it should be fine, and we don't know the details of your setup so none of us can do the job remotely. Whoever you do get will have to go over all of the calculations, etc, any way.

Good luck!

Ok so it's a case of regulations not catching up with current technology, which is understandable given that there'll be plenty of people who still use the old tech.

Poor choice of words lol. What I should say is that with the knowledge I have I can filter out the cowboys who'll promise the everything and not deliver on anything, I'm sure you can agree there are plenty of them around who make finding a quality electrician much more difficult.

No that is a vicious price .
Depending on the size of bore , ground type , if the pits have been prepared for us and distance to travel , we start at £250 plus vat upwards.
If you were local to Buckinghamshire your one would be £250 or £350 if we dig the pit .

I actually live near Skegness and commute each day at the moment to our yard in Buckinghamshire , my day tomorrow consists of a 7:30 am meeting in Milton Keynes then Thame then Southampton then Winchester then Lechlade then Lambourn , back to Oxford and finally home again to Lincolnshire , so you are not that far away to be honest if you wish to pm me some more Pacific information I could take a look and maybe price it for you .

I think it might be a bit too much of a drive. I'll try to find other prices. Thanks for the offer though, I will keep it in mind.

If you can get a large enough duct put in then all your problems go away, you can put in whatever size of SWA power you want and a few networks cables to finish the job! :)

Well, maybe not total price...

If I can afford to do it and get a bigger duct installed then, I'll probably just go crazy and throw a 35mm cable in so it can handle 100A lol.
 
If I can afford to do it and get a bigger duct installed then, I'll probably just go crazy and throw a 35mm cable in so it can handle 100A lol.

I know you are joking above, but you can't have 100A to your garage, unless you get a dedicated supply. The supply to your garage has to be lower than your main fuse rating.
 
No worries , but your first price was way off .
I've just got to the Oxford job so off home soon , should be back by 10pm. ?
 
Already said by @Spoon is to allow for your supply limit :)

If you really want to be sure that a worst-case garage fault can't take out your main fuse then you would generally want it fused at less than 60% the DNO rating (checking selectivity would need a bit more care than just that) so you would look at 50A/63A max on a 100A supply fuse, etc.

But out of curiosity you can look at the following for other cables sizes and your 50m run below (based on 2-core cable using Prysmian data sheet):

Drop % =​
3​
Vdrop​
6.9​
V​
Length​
50​
m​
CSA (mm^2)​
Dia (mm)​
Res (mOhm/m)​
R (Ohm)​
Max on VD​
Max 4D4A (70C)​
Max I (A)​
1.5​
11.8​
31​
1.55​
4.5​
22​
4.5​
2.5​
13.2​
19​
0.95​
7.3​
29​
7.3​
4​
14​
12​
0.6​
11.5​
37​
11.5​
6​
14.4​
7.9​
0.395​
17.5​
46​
17.5​
10​
18​
4.7​
0.235​
29.4​
60​
29.4​
16​
19​
2.9​
0.145​
47.6​
78​
47.6​
25​
22​
1.9​
0.095​
72.6​
99​
72.6​
35​
24​
1.35​
0.0675​
102.2​
119​
102.2​

Drop % =​
5​
Vdrop​
11.5​
V​
Length​
50​
m​
CSA (mm^2)​
Dia (mm)​
Res (mOhm/m)​
R (Ohm)​
Max on VD​
Max 4D4A (70C)​
Max I (A)​
1.5​
11.8​
31​
1.55​
7.4​
22​
7.4​
2.5​
13.2​
19​
0.95​
12.1​
29​
12.1​
4​
14​
12​
0.6​
19.2​
37​
19.2​
6​
14.4​
7.9​
0.395​
29.1​
46​
29.1​
10​
18​
4.7​
0.235​
48.9​
60​
48.9​
16​
19​
2.9​
0.145​
79.3​
78​
78.0​
25​
22​
1.9​
0.095​
121.1​
99​
99.0​
35​
24​
1.35​
0.0675​
170.4​
119​
119.0​
 

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