Help on mains power

[mgnelec09]

Hi,

went to to look at a job last week where the builder proposes that the new electrical installation will require 135amp three phase.

However the the main incomer to the site only seems to be 100 amp three phase and a 25 mm incomer.

i have calculated that the run from the main incomer to the new building will be around 80 Mtrs which will require a 35 mm 4 core swa

would I be right in saying that the mains would need upgrading to 250amp to split the existing 100 amp main distribution board up from the new proposed building on 134 amp.

Surely this his will mean the main incomer will need upgrading to around 75 mm?

any advice appreciated. Thanks steve

 

[Octopus]

Why is the "builder" proposing a 135A supply. Has HE DONE THE CALCS??

 

[Darkwood]

Who's calculated the 135amp...

What is the demand of the existing?

Not sure how you think a 35mm 3ph supply will be adequate as it doesn't equate without cable calcs....

Please show your calcs so we can help/guide you...

PS you need to establish your OCPD type if your using HRC fuses you will be limited to the size range available i foresee you requiring a 160amp 3ph supply to new build.

You seem a bit out of your comfort zone here i would be tempted to get someone in who is experienced with this kind of work and work in tally with them this way you get the essential onsite experience required ... trying to do this off a forum can be hap-harzardous as any assumptions, mis-information or missed info can be crucial to design.

 

[mgnelec09]

Hi,
the new building is a two storey prefabricated cabin style building with electric heating throughout, they have the manufacturers have spec of 135a 3 phase for max demand.
The he main incomer goes into the main building at 100 amp 3 phase.
I have had a clamp ammeter on each phase at busiest times of the day which comes back at with around 70 amp per phase.

Who's calculated the 135amp...

What is the demand of the existing?

Not sure how you think a 35mm 3ph supply will be adequate as it doesn't equate without cable calcs....

Please show your calcs so we can help/guide you...

PS you need to establish your OCPD type if your using HRC fuses you will be limited to the size range available i foresee you requiring a 160amp 3ph supply to new build.

You seem a bit out of your comfort zone here i would be tempted to get someone in who is experienced with this kind of work and work in tally with them this way you get the essential onsite experience required ... trying to do this off a forum can be hap-harzardous as any assumptions, mis-information or missed info can be crucial to design.

 

[Darkwood]

Would it not be better all round to have a new DNO supply to the new build instead of having the DNO upgrade existing only for you to have to run a possible 160amp / 70 - 120mm supply depending on install methods ... you have given us the heating load only any nothing else what about power and lighting .... you are asking us with limited info yourself ... you need to have a site meeting and also way up the expected demand yourself an not from a builder...

Ill re-iterate i fear this is well out of your comfort zone and shouldn't be attempted by scraping info of a forum you be best getting someone in and working alongside them giving you valuable insight and experience...

 

[mgnelec09]

Hi, some good advice.
The demand has been set by the manufacturer of the pre fab cabins as they come ready built with lighting power etc.

My cable calcs have been estimated via a cable calculating program as if I'm honest not sure off top of my head.

By DNO I presume you mean the main distribution source.

I agree, it is not just a quick solution to get this sorted.

what they have done is ordered the cabins thinking the 80 meter run on a 25 mm 4 core is ample. They just need it powering up.

However by by getting these figures on Friday and knowing the whole site only has 100 amp three phase, something wouldn't add up.

I agree it needs investigating further, we are an Niceic approved contractor but don't want to give them false info as there could be a lot at stake.

Who would be best to make the decision? Should the landlord seek further investigation?






If I'm h

Would it not be better all round to have a new DNO supply to the new build instead of having the DNO upgrade existing only for you to have to run a possible 160amp / 70 - 120mm supply depending on install methods ... you have given us the heating load only any nothing else what about power and lighting .... you are asking us with limited info yourself ... you need to have a site meeting and also way up the expected demand yourself an not from a builder...

Ill re-iterate i fear this is well out of your comfort zone and shouldn't be attempted by scraping info of a forum you be best getting someone in and working alongside them giving you valuable insight and experience...

 

[shanky887614]

Hi, some good advice.
The demand has been set by the manufacturer of the pre fab cabins as they come ready built with lighting power etc.

My cable calcs have been estimated via a cable calculating program as if I'm honest not sure off top of my head.

By DNO I presume you mean the main distribution source.

I agree, it is not just a quick solution to get this sorted.

what they have done is ordered the cabins thinking the 80 meter run on a 25 mm 4 core is ample. They just need it powering up.

However by by getting these figures on Friday and knowing the whole site only has 100 amp three phase, something wouldn't add up.

I agree it needs investigating further, we are an Niceic approved contractor but don't want to give them false info as there could be a lot at stake.

Who would be best to make the decision? Should the landlord seek further investigation?






If I'm h

80m? Not a very big supply from a 25mm especially when you take into account install method and distance.

 

[mgnelec09]

80m? Not a very big supply from a 25mm especially when you take into account install method and distance.

I know that's the point. The existing is about 65 metres on a 63amp feed, hence the cable.

They were here hoping to do the new pre fab on the same cable, I was at site on Friday doing some maintenance and they asked me to look into it.

 

[guest119]

throughout, they have the manufacturers have spec of 135a 3 phase for


Is that then 135/3 = 45a per phare additional load?


Boydy

 

[Knobhead]

What the hell is in these buildings? 135A equates to 93KVA!

 

[bendjeddou]

i think you can supply new installation with out modify old installation, but it shouldn't works in same time

 

[Engineer54]

i think you can supply new installation with out modify old installation, but it shouldn't works in same time

Hmmmm, ....Maybe in Algeria!!

 

[Darkwood]

That's up there with the most idiotic answers ..... so i second your comment E54!

Tell you what why not put it all on a 13amp extension as long as you only dont turn anything on except the alarm system.

 

[UNG]

Hi, some good advice.
The demand has been set by the manufacturer of the pre fab cabins as they come ready built with lighting power etc.

My cable calcs have been estimated via a cable calculating program as if I'm honest not sure off top of my head.

By DNO I presume you mean the main distribution source.

I agree, it is not just a quick solution to get this sorted.

what they have done is ordered the cabins thinking the 80 meter run on a 25 mm 4 core is ample. They just need it powering up.

However by by getting these figures on Friday and knowing the whole site only has 100 amp three phase, something wouldn't add up.

I agree it needs investigating further, we are an Niceic approved contractor but don't want to give them false info as there could be a lot at stake.

Who would be best to make the decision? Should the landlord seek further investigation?

If I'm h

Get your qualified supervisor to sort this as he is the one who will ultimately sign off the job

 

[Knobhead]

Get your qualified supervisor to sort this as he is the one who will ultimately sign off the job

Good point UNG

Again, an armature having gleaned a few bits from here quotes a NIC inspector in they’re defence and is uncovered. As they should be.

 

[bendjeddou]

hahaha... yes in algeria it works good, because we have many heads have same thinking like our cases they want the production with zero tools