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Cable size meter to building 72M


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I've got an 'electrician' wiring a 10 room building and just want to check cable size needed to run 72m from the meter to the building. At the building the cable will then split off to each room via its own meter. Each room has its own CU supplied with 10mm cable (rooms have 1 aircon max 20,000 BTU and hot shower, say 4000kw).

What size cable should he be fitting for the 72m run from the electric meter point to the building ? Cable will run underground in protective pipe.

Thanks.

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Thai cable is not the same quality so it's very hard to calculate the real thickness.   And also those transformers mounted on poles, they explode regularly or they start melting and drippin

From the OP, 10 rooms, each with it's own meter. I think it safe to assume each room is a longer term rental.    As such, all or most AC likely at the same time, and all or most hot showers

How will the rooms be configured?  AC?  Hot shower?  Kitchen(ette)?  30A per room seems like maximum demand potential that might be very unlikely to occur.  Reality might be 50A for the entire buildin

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1 hour ago, Youlike said:

Thai cable is not the same quality so it's very hard to calculate the real thickness.

 

And also those transformers mounted on poles, they explode regularly or they start melting and dripping liquid metal.....it's not the same quality....

 

Best would be to order it from a reliable country with real standards and real electricians.

 

Or just move there. 

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2 hours ago, Youlike said:

Thai cable is not the same quality so it's very hard to calculate the real thickness.

 

And also those transformers mounted on poles, they explode regularly or they start melting and dripping liquid metal.....it's not the same quality....

 

Best would be to order it from a reliable country with real standards and real electricians.

 

The woodworker will blow a vessel when he sees this post, you'll be made to stand in the corner for at least two hours.

 

PS

Before the gurus arrive it might be a good idea to know how many phases are available.

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How big is the intended meter?

How many phases?

 

Making some assumptions.

 

About 6kW per room = about 30A.

 

10 rooms x 30A = 300A so 100A per phase on 3-phase. A 30/100 3-phase supply would be the ticket taking into account diversity.

 

75m @ 100A and 3-phase would be 35mm2 copper or 50mm2 aluminium.

 

But do verify with your supply authority, they may have different requirements.

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17 hours ago, Crossy said:

How big is the intended meter?

How many phases?

 

Making some assumptions.

 

About 6kW per room = about 30A.

 

10 rooms x 30A = 300A so 100A per phase on 3-phase. A 30/100 3-phase supply would be the ticket taking into account diversity.

 

75m @ 100A and 3-phase would be 35mm2 copper or 50mm2 aluminium.

 

But do verify with your supply authority, they may have different requirements.

Thanks Crossy. Will check with electric authority.

Meter isn't fitted yet - they put in a temporary single phase one for the construction.

How to determine size of intended meter - are you saying should be 30A based on above ?

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How will the rooms be configured?  AC?  Hot shower?  Kitchen(ette)?  30A per room seems like maximum demand potential that might be very unlikely to occur.  Reality might be 50A for the entire building for a peak load.  The incomer cables should be sized for worst case but 30/100 3-phase seems a bit of overkill to me.

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1 hour ago, regedit said:

Meter isn't fitted yet - they put in a temporary single phase one for the construction.

How to determine size of intended meter - are you saying should be 30A based on above ?

 

Check what they can provide without you going to the expense of your own transformer. They may only be able to provide a 15/45 3-phase (depends where you are).

 

In reality, as @bankruatsteve notes 30/100 may be overkill, but if it's available it will cost only slightly more.

 

The UK network operators use something like 2kW (10A) per home when sizing supplies but that relies on diversity over hundreds of dwellings (each home would likely have a 60 or 80A incoming fuse). With only 10 units the possibility of everyone running the A/C and shower at the same time is much greater.

  

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On 9/11/2020 at 12:26 PM, Crossy said:

 

Check what they can provide without you going to the expense of your own transformer. They may only be able to provide a 15/45 3-phase (depends where you are).

Yes, turns out they will prove 3 phase 15/45 meter. Am I still looking at 35 sqmm cables ?

Also, are the phases are setup with 3 rooms on 1, 3 rooms on 2 and 4 rooms on 3, assuming all rooms expected to have same consumption ? 5 rooms are on an upper floor.

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15 minutes ago, regedit said:

Yes, turns out they will prove 3 phase 15/45 meter. Am I still looking at 35 sqmm cables ?

Also, are the phases are setup with 3 rooms on 1, 3 rooms on 2 and 4 rooms on 3, assuming all rooms expected to have same consumption ? 5 rooms are on an upper floor.

 

You should be able to drop to 16mm2 copper or 25mm2 aluminium subject to approval by the PEA. The aluminium is less likely to wander off in the night 🙂 

 

Try to balance your loads across the 3-phases although precise balance isn't necessary or practical in a domestic environment. For example put your main bedroom A/C on one phase then the other 4 bedrooms split beween the remaining two, 2 rooms on each.

 

Try to manage the power outlets and lighting so that all areas get at least something if a phase goes out (the most common failure mode).

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6 minutes ago, Crossy said:

For example put your main bedroom A/C on one phase then the other 4 bedrooms split beween the remaining two, 2 rooms on each.

Crossy, in this case the OP says he has a 10 unit (apartment?) building.  5 rooms down, 5 rooms up.  Divy the phases by rooms.  😎

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Just now, bankruatsteve said:

Crossy, in this case the OP says he has a 10 unit (apartment?) building.  5 rooms down, 5 rooms up.  Divy the phases by rooms.  😎

 

Yeah, I missed that bit of the history 🙂

 

Each room with it's own single-phase board. Outside/public area lighting split beween the phases.

 

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