couple of questions 3 phase / single phase!

[daniely87]

hey, a couple of questions regarding electricity supply
1. if the mains board is 3 phase and has 3x100Amp fuses, can you put a 100A MCB on each of the phases? currently we have 63A MCB's, occasionally they may trip, so we will put them up to 80A MCB's, but i was wondering how over/underrated the 100A fuses the electricity board put in are? could i get away with a 100A MCB or is it too likely to blow the main fuses?
2. If i have a thick 3 core cable..i can run 3 phases down it?, i have a 3 phase supply entering my field to a box, where it branches off to other parts of the field.....i have run the new cable to the building we are in the middle of constructing..., someone today suggested a 3 phase heat pump...no one else has......is it possible to run 3 phase supply down the 3 core cable (very thick) AND use the remaining electric from the 3 phases / convert back to single phase? (if that makes any sense)
don't worry i am not going to attempt any of this myself! just electrician isn't back for a few days and i need to let the heat pump man know ASAP if 3 phase is available
thanks in advance!!

 

[ColJack]

are you sure there are 100A fuses in there? just because it's marked 100A on the outside doesn't mean it's not a 63A or 80A fuse inside..

if it is 100 then yes, you can put 100A mcb on.. but what is it for? 300A is a lot..

2. no.. if you need single phase as well then you need 4 core for the neutral..
and how thick is this cable you have installed, how long is it, what's it feeding, how many amps do you think you'll need, how deep was the trench you ran it in and where did you run it?

 

[daniely87]

are you sure there are 100A fuses in there? just because it's marked 100A on the outside doesn't mean it's not a 63A or 80A fuse inside..

if it is 100 then yes, you can put 100A mcb on.. but what is it for? 300A is a lot..

2. no.. if you need single phase as well then you need 4 core for the neutral..
and how thick is this cable you have installed, how long is it, what's it feeding, how many amps do you think you'll need, how deep was the trench you ran it in and where did you run it?

thanks for the quick reply, definately 3x100 fuses, thats what all the EDF energy paper work says and thats what we paid for, even had to pay for transformer upgrade which cost about £8,000 although it did upgrade electric supply from 60-100 at some other properties too! im 110% sure though as the amount of electricity points we run off the other supply, we wouldnt have been able to if they were only 60A and the electricians run numerous 60A breakers on that board too, the reason i asked about 100A MCB on 100A mains fuse was because they said i should try to keep under it as i don't want to blow the fuses...but thats good, point 1 is sorted!!!
its on our campsite, we have 2x3 phase supplies....this particular cable is for a new building, the heatpump alone may be 20kw output, so about 30 amps input at max load, although we were told today of a 3 phase one that may be better than the single phase we were originally going for, i think the cable is about 1.25 to 1.5 inches in diameter, can measure tomorrow, a lot thicker than we use on the normal single phase electric point runs, the cores look as thick as the tails , its about 55 metres from our electricity hut, its 3 foot down!
ok so we have a 3 core cable....and want to run lighting / hand dryers / hair dryers / a 3 phase heat pump from it? any ideas? thanks again!

 

[Spark123]

It isn't just a case of upping the MCB, you need to know that the circuit is suitable for the altered circumstances.
Are you sure that an MCB 63A> is available for your board?

Your 3 core cable doesn't sound suitable to me - to me you'd need a 4 core to provide a neutral for your single phase (and possibly the 3 phase) supplies.

Sounds like you'd be better off holding back for your electrician to return or seek advice from another electrician who can visit the site.

 

[daniely87]

It isn't just a case of upping the MCB, you need to know that the circuit is suitable for the altered circumstances.
Are you sure that an MCB 63A> is available for your board?

on the 2 runs which i plan to get them to put 100A MCB's on, the cable goes to another box half way along the run, where it is then divided, another very thick cable though, capable of 100 amps i believe...

and yea, they told me an 80A was available for my board now, and i have just been to Hager website, where 80, 100, 125 are available for domestic / commercial and looks identical!
is there any easy way to look at the cable and tell what it is capable of? should it be written on it? im 99.9% sure it can cope with it, again i will let them make the decision, just i am trying to kill 2 birds with one stone, on one post! getting my latest 2 runs of electric points increased and sorting my newest facility block!! thanks again

 

[ColJack]

20KW is about 87A.. unless you were talking about the 3 phase one.. then 30A is about right per phase..

this is not really a DIY subject though and your electrician is ina much better position to tell you what your system is capable of as he can see it and we can't..

 

[daniely87]

20KW is about 87A.. unless you were talking about the 3 phase one.. then 30A is about right per phase..

this is not really a DIY subject though and your electrician is ina much better position to tell you what your system is capable of as he can see it and we can't..

thats the output its liek 3-400% efficient though, yea i sort of realised this isnt too DIYified but this forum is full of wonderful people
just found single phase to 3 phase converters oh dear, i think its best i wait til electricians get back, thanks again everyone