3 phase ext lead ?

[sparkysy]

Mmm I am always dubious at best about online calculators for cables some of them are way off and some have soo many options that only qualified people understand what to put in to get the correct answer out. I use the regs and calculations within to check I am correct.
I would think 240mm would be sufficient off the top of my head but without proper calculations I would not say it definitely is.
That is a meaty supply so switchgear and cable is not going to be cheap. Moulded case dis boards are very expensive as are the mccb's to go in them! Sounds like a good project though I like a cable with a bit of girth!!

 

[brightspark]

[QUOTE="sparkysy, post:! Sounds like a good project though I like a cable with a bit of girth!![/QUOTE]so do I as long as someone else is installing it

 

[sparkysy]

used to do a lot of heavy cables on projects and loved it, I could write a book about some of the things that went on, Great times! Longest cable run I was ever on was 860m of 120mm 4c that was for a grain shed, that was a serious wedge of copper and money and some major machinery and manpower to manipulate it into position!

 

[timgunn1962]

Any lincs as to where to get this HO7 cable?

Or what to ask for when trying to order some.

Thanks for the reply’s..

https://www.online-cables.co.uk/

Near the bottom of the page: H07RN-F cables, click on the number of cores you want and it'll show you sizes and prices-per-metre.

No affiliation, except as a satisfied customer.

 

[Beeezer]

https://www.online-cables.co.uk/

Near the bottom of the page: H07RN-F cables, click on the number of cores you want and it'll show you sizes and prices-per-metre.

No affiliation, except as a satisfied customer.

Thanks.

 

[knighty]

Did you change the default voltage to around 415v?

EDIT you can also run parallel cables.

240v says 240mm csa, 415v says 70mm csa

I was assuming 240v because it's 240v each phase?

the distribution box it's leading to will have 4x 30hp freezer compressors, plus about 20hp of smaller fridge/freezer compressors, plus 30hp air compressor... I don't really want to skimp on the cable feeding it

 

[knighty]

Mmm I am always dubious at best about online calculators for cables some of them are way off and some have soo many options that only qualified people understand what to put in to get the correct answer out. I use the regs and calculations within to check I am correct.
I would think 240mm would be sufficient off the top of my head but without proper calculations I would not say it definitely is.
That is a meaty supply so switchgear and cable is not going to be cheap. Moulded case dis boards are very expensive as are the mccb's to go in them! Sounds like a good project though I like a cable with a bit of girth!!

`
any chance you could do some calculations and tell me for sure?

my electrician is good... but he's not used to working with stuff this big

I phoned a few that work with bigger stuff but they weren't keen, I need to dig a trench through my yard right in front of the gate to bury the cable... planning to do that on a bank holiday weekend or over christmas/new year so I can have it concreated again ready for work asap


I'd get the new supply brought in right where I need the high power stuff... but it's 3m in the air in a steel framed building above a freezer... doubt grid people will be keen on that :-(

 

[sparkysy]

Hi @knighty
I will have a look tomorrow if I get time, my workload is quite hectic at the moment! I think 240mm would do it but just want to double triple check! if it will you could always say use 2 lots of 120mm 5c to make it easier to handle and terminate its still not going to be small though!

 

[knighty]

Two lots of 120mm might be easier... I'm just thinking in and out of the distribution boards might be a bit messy.

There's no hurry yet.... got two quotes from grid people, one for 200amp one for 300amp (had to pay £150 per quote)

Said I'll go ahead with the 300anp supply.... yo be told I now need a more advanced quote for £350

Guess the first quote/cost is just to stop time wasters? Idk.

 

[sparkysy]

Hi again @knighty

Right I have had a look and I think that you will get away with 240mm if it is 90 degree xple swa as in table 4E4A below, over that distance you will have about 2.7v drop so at the far end 397v that is in duct the entire length.
Table

If it was me doing the job I would personally go for 300mm to be absolutely sure, as I don't know all the details of the main incoming supply parameters or what loads you will be running.
Best thing to do is get whoever is installing and signing off the installation to calculate again as they will be taking responsibility for the work.
I would also ask what size supply tails the DNO or service provider require installing for connection, just as I have had issues with supply connection on a number of occasions!

 

[knighty]

I didn't realise there was such a big difference between the cable for buried vs clipped to a wall!

I'll price up 240mm... it'll probably be crazy....

I'll need about 60m of 240mm... a quick google isn't giving me prices for 5 core only 4 core, but that's £60/meter -(

not much choice tho, if I need it I need it

 

[sparkysy]

Yes it's a fair increase in size, yeah about £60-80per meter for 4 core sounds about right, 5 core would probably be about £100 ish + vat! is there a local friendly wholesalers near you that might do you a deal?
The other gear you need will not be cheap either!

 

[WorkshopChris]

Yes it's a fair increase in size, yeah about £60-80per meter for 4 core sounds about right, 5 core would probably be about £100 ish + vat! is there a local friendly wholesalers near you that might do you a deal?
The other gear you need will not be cheap either!

That's what I was thinking with the price of all the associated switchgear once you get to over 100a price bracket, I would imagine a good independent supplier might offer competitive pricing.

I'll need about 60m of 240mm... a quick google isn't giving me prices for 5 core only 4 core, but that's £60/meter -(

not much choice tho, if I need it I need it

Is there a reason you need 5 Core? You should be able to get a good price on a single for your earth, does it need to run directly into the panel rather than a dedicated earthing bar?

Do you have a copy of the City electric catalogue, it should give you a base price for some of the heavier gear.

 

[sparkysy]

Thats it over 100a and it's starting to get very pricy indeed, probably best to get a quote on all the bits you need together as they might give you a better discount!
You could use 4core and use a separate earth, not sure if the swa would be big enough to comply on that size that is another equation again!

 

[mtt.tr]

i have to ask what are you powering at the end of this cable? whats the incoming arrangement?

might it be cheaper to ask power network to install a second supply direct to what ever you are doing ?


**edit**
just looked at ukpn costs, that wont be cheaper

 

[WorkshopChris]

You could use 4core and use a separate earth, not sure if the swa would be big enough to comply on that size that is another equation again!

Personally whether or not if it does require a separate earth I wouldn't want to be relying on it at that size, seen to many poor readings from damaged cables on installation sitting in water degrading the SWA.

 

[J1nx]

Two cores per pole is a no brainier here, probably cheaper and easier. The benefit of two smaller cores current carrying capacity over a single large will make a big difference here, you will probably get away with 70 or 95mm.

 

[knighty]

replying to lots of people but not quoting everyone because this post will get really long...

can't get the supply right where I'm going to use most of the power, it's 3m up in the air in a steel building... but it's not really a building, there's a freezer on the floor and this goes around it, it has a roof and a back wall, three other walls are mesh to let air into the fridge.freezer compressors

two new freezers going on, one blast freezer one for storage, 2x 30hp compressors on each (rated at 55amps running each) - there's 220amps... then there's a few smaller compressors, a big air compressor... then there's small stuff attached

I'll talk to my electrician, see if I can run all this stuff from it's own earth... then the earth run would only need to be 4m.... I can't remember the rules, can I join the earth to the (exposed) steel frame building?

2x 70mm looks like it might be the way to go... I'm going to have another good look/think and see if I can surface mount it instead... it'll add about 20m to the length but the smaller cable should more than make up for that