New supply

[ruston]

I'm impressed with your engineering skills and equipment too.

 

[Peter44444]

Thanks John that's a heck of a lot to think about. But all great information. I'm now going to talk to my electrician, work out my usage and diversity and in particular talk about three phase or single phase. I think I would be OK on a new 100A single phase supply for the yard. And keep my old supply for domestic. I am a one man band and would only be using one 16A socket at a time. I could forget the 32A welder if needed and if I had four customers running angle grinders or boiling kettles at the same time that would be a very rare event. I will put in an application for three phase though as that would be the ultimate for the site and if I can afford it that's what I'll go for.

 

[apprentice87]

Hi Peter,

If you ask for a three phase supply, you will find it is only very slightly more than a single phase one. It makes no difference to the DNO at all, BUT and it is a VERY big but, they would MUCH rather give you a three phase 60A supply than a 100A single phase one, because they have to spread the load as equally as they can over all three phases for reasons i will not bore you with!!

From your point of view three phase would be much better for the following reasons..

1, A 60amp three phase supply would be the same as having THREE 60amp single phase ones. You would in effect have a 180 amp single phase supply..

2, You could run three phase equipment which, apart from being cheaper, is FAR better, AND simpler, AND more reliable, than single phase stuff. If i showed you a single phase motor running, then a three phase one, you would be amazed at the difference, you would thing the single phase one was faulty....

3, You could in the future, build three sheds or houses, then lead a phase [and install a meter] in each and have your own rented out industrial estate!! [why work if someone will give you rent!!]

4, Finally, if you only had a 60A three phase supply, you will find that not only will you have the equivalent of 180A single phase, the 300m cable itself is going to be MUCH MUCH cheaper..

john...

 

[apprentice87]

What size cable do you have running the 300 metres now?? According to me you would need a 300mm one???? I cannot even find 300mm 2 core, but the 3 core would be about £20,000 and the cable would weigh about 4 tons....

The three phase 4 core one though [for 60a], would only be 70mm, would cost about £5000 and would weigh about 1 1/4 tons.. Would be just under 1 1/2" diameter compared to over 2" for the single phase 100a one AND, you would still have nearly three times the power.....

It is a no brainer..

john..

 

[Lurch]

According to me you would need a 300mm one????

Where do you get that from? You seem to be getting around double what I would say would be needed.

 

[Tony S]

What size cable do you have running the 300 metres now?? According to me you would need a 300mm one???? I cannot even find 300mm 2 core, but the 3 core would be about £20,000 and the cable would weigh about 4 tons....

The three phase 4 core one though [for 60a], would only be 70mm, would cost about £5000 and would weigh about 1 1/4 tons.. Would be just under 1 1/2" diameter compared to over 2" for the single phase 100a one AND, you would still have nearly three times the power.....

It is a no brainer..

john..

I've used 300mm high conductivity 2c SWA for DC, it cost an arm and a leg to have made.

Where do you get that from? You seem to be getting around double what I would say would be needed.

I've given up doing any calculations for this topic.

 

[apprentice87]

Where do you get that from? You seem to be getting around double what I would say would be needed.

Hi Lurch, I know!! I did the calcs for 3% volt drop on 100A over 3oo metres several times.. I though it could not be right... I went on one of the cable makers websites with a calculator, entered 100A single phase 300M and they came up with the same..

This one here..

http://www.doncastercables.com/technical-help/

Here is how i worked it out by hand as it were.. Please have a look and see if it looks right......????? cos 300mm cable is huge!! [well, to me it is!!]

3% x 230 = 6.9v /1000 = 6900mV

100A x 300m = 30,000

6900/30,000 = 0.23 mV/A/M

Work it the other way.. 0.23mV x [100A x 300m] = 6900mV = 6.9V

Look on a cable chart; and 300mm is 0.21 mV/A/M

Am i missing something?? [remember i am not an electrician!!]

john.,.

 

[Andy™]

dont forget if you use your entire VD on the submain, you will be left with nothing at the DB end for the final circuits and submains to other buildings

 

[Lurch]

Am i missing something??

Yes and no. There's various different ways of keeping the VD within acceptable limits and a lot depends on the the actual load/design current of the final circuits, and also you might only apply a small percentage of the VD to the final circuits or sub-main. You can also relax the VD calcs for sub-mains a bit, but as this thread is still somewhat vague it is hard to give an exact worked example, so you may be OK with a 120mm² cable, or you may need a 300mm². It all depends on various site specific variables and how the person doing the design actually designs it. I'd probably look at working the design a few times until it works with a 120mm² cable as this is a fairly obtainable and standard size, but then again sometimes you can't.

 

[Peter44444]

My family member that just had their 100A SP supply in to the new house had a 185mm 4 core cable put it by the DNO the length of run was 298m helpfully! All buried. 

 

[Peter44444]

Three phase would be great but I will see how the costs work out. If they're going to bill me for a transformer it might be too expensive. If it's just another 100A SP supply run from the current transformer 30m to where I can put a new box in it might be very cheap. I'll have to see how it goes.

 

[Sidewinder]

My family member that just had their 100A SP supply in to the new house had a 185mm 4 core cable put it by the DNO the length of run was 298m helpfully! All buried. 

Peter,

The DNO do not work to BS7671, so comparing what happens before & after the cutout/meter is irrelevant.

However, if, the cable is 4 core, then they have either doubled up on cores, or allowed for a TN-S TPNE supply which is unusual, but not impossible.

If they have doubled up then they have 370mm sq of copper or ali going to the property.

A normal 60/80/100 A domestic supply is given probably 40A on the DNO side, the rest is covered by diversity.

For a boat yard business, I would seriously look at 3ph & separate to the dwelling house.

 

[Peter44444]

If you ask for a three phase supply, you will find it is only very slightly more than a single phase one. It makes no difference to the DNO at all, BUT and it is a VERY big but, they would MUCH rather give you a three phase 60A supply than a 100A single phase one, because they have to spread the load as equally as they can over all three phases for reasons i will not bore you with!!

sorry I miss read this... I get it now... I think. They won't be very keen on taking 2x100A supplies off one of their phases. Even though the SP transformer is already fitted they might be more interested in replacing with a TP transformer as it would be balanced across then.

 

[Sidewinder]

If you ask for a three phase supply, you will find it is only very slightly more than a single phase one. It makes no difference to the DNO at all, BUT and it is a VERY big but, they would MUCH rather give you a three phase 60A supply than a 100A single phase one, because they have to spread the load as equally as they can over all three phases for reasons i will not bore you with!!

sorry I miss read this... I get it now... I think. They won't be very keen on taking 2x100A supplies off one of their phases. Even though the SP transformer is already fitted they might be more interested in replacing with a TP transformer as it would be balanced across then.

They will be a lot less than "not very keen", pound to a penny they will refuse point blank, too much imbalance I suspect.

You really need to ask UKPN, being in South Wales I only know one UKPN Engineer, and he is right down the SW of their area.

 

[apprentice87]

Hi Peter,

The 185 mm cable the DNO put in, would not have been a service cable to the house. They are a single core CNE type thing of 35mm and i think the max length is about 50 metres????. They have put in an extension to their LV mains. This is well good, because if your mate wants three phases. or another single phase supply, the thing is already there. I woud have been WELL pleased!!! Do all your mates have 300 yard front gardens then??

john..

 

[NozSpark]

The yacht club that I was a member of had about 50 boats laid up..... The biggest and mostly used loads were heaters.... Ok, so they used the odd grinder, drill and welder and kettle,,, but nearly all of them wanted a heater running 24/7 in the winter....

And they have a shed/workshop ,,,,, all running off a SP 100A supply

No moored boats were allowed an electric supply as they weren't allowed to moor up against the wall due to its instability

BTW they get 2 cranes in for lift out/in