120mm to 25mm connection

[tony rowan]

Hi, I have a domestic job coming up that requires a 100A supply but it's 260mts from where the metered supply will be installed.
120mm 3 core supply SWA cable (260m long, 120mm 3 core due to voltage drop)
My problem is, how do I connect the 25mm meter tails to the 120mm SWA cable at the meter end & also how would I terminate back to 25mm tails at the consumer unit end?
I know that I could use a300A 3 phase TP & N fused isolator but trying to find a cheaper option for the client.

I have considerd a bus bar chamber or 300A TP&N isolator?

any suggestions would be appreciated

Regards
Tony

 

[pc1966]

Found the fuse sizes here:

What type of replacement fuse links can be used with Quadbreak fuse switches? | Schneider Electric UK

Looking at one of the data sheets for LV fuses (Mersen BS88 LV Fuse Links & Fuse Holder) it looks like you can downgrade a B3 size fuse with a B2, B1, or B1C giving you ratings all the way down to 32A (though I would really double-check the fuse physically fits, etc, before trying it).

 

[brianmoooore]

Overcomplication going on here. It may be a cable rated at 230A or so, but it will be running at an absolute maximum of 100A, so change at each end to a short length of 25mm2 in a resin filled buried joint, then terminate in 'normal' domestic gear at each end.

 

[westward10]

I'm not seeing anything complicated and less joints the better.

 

[JD6400]

Although the Glasgow range or the Schneider boards look the dogs dangles , don't forget he is only dealing with 100 amps at the end of the day.
Those inline reducers with heat shrink in a suitable enclosure with the joint coming down to 25 mm tails for the final connections , are likely to be at least £££s cheaper if not possibly ££££s.

I have just realised that I did not mention that they can handle large difference's in CSA between sides.

 

[brianmoooore]

Don't disagree that the less joints in a circuit, the better, but properly made, resin encapsulated joints are at the higher end of the reliability spectrum.

 

[westward10]

I think the OP is busy rolling out his 260m of cable?

 

[westward10]

Don't disagree that the less joints in a circuit, the better, but properly made, resin encapsulated joints are at the higher end of the reliability spectrum.

Can imagine doing a periodic on it without any info on the cable except a 25.0 coming out of the ground each end and wondering why your Zs is so low for an imagined 260m of 25.0??

 

[pc1966]

Can imagine doing a periodic on it without any info on the cable except a 25.0 coming out of the ground each end and wondering why your Zs is so low for an imagined 260m of 25.0??

Well if it is for a certain Dr Who then maybe there is tardis technology involved

 

[pc1966]

I think the OP is busy rolling out his 260m of cable?

Hard work I'm sure! A quick check has 120mm 3-core as about 5.1kg/m so total of just over 1.3 tonnes of wire to be laid out.

 

[freddo]

We recently pulled in 185M of 4 core 120mm swa on high level ladder. Certainly not an easy task!

 

[UNG]

This is one of those jobs that has the possibility / probability of ending up in a lot of finger pointing
There are some questions that need to be asked like when it comes to the EIC who is going to put their name on the design, when the installation has issues due to exceeding the volt drop limits who will take the blame

my question was not how to calculate voltage drop but for suggestions on how to terminate from one size to the other

I think without people posting concerns about the volt drop and size of cable to be used it may be seen as they are accepting the design of others is compliant while they are offering advice on the the question you asked

but there are options & maybe I've not considered them all

IMO there are options not least walking away from a job with a recipe that has all the ingredients of an acrimonious ending because of the issues that this thread has highlighted a simple one a few years down the line what happens if the property is sold and the EICR done as part of the sale is found unsatisfactory You can do many excellent jobs that no one will hear about but the one that goes wrong everyone will hear about it

 

[pc1966]

£40K was the cost for mains supply to the source. The client was told that he could save money & build a meter box on the edge of the property & install his own supply from that source. This was suggested by REC. This is not an install that I relish...

Were the cable calculations done by the DNO?

If so it might be reasonable to assume the system is what they would have done had the cut-out been installed at the property so your end of sub-main voltage remains within ESQCR specifications.

 

[mechelec]

Get the customer to get a quote from DNO to install up to where you really want the incoming cutout. If the customer is willing to dig the trench you may find there is not much in it cost wise and it will be done correctly.