![]() Should still not be a big issue as long as you distribute the single phase loads on/across the individual 3 phases as much as possible. Noddybrian wrote:Thanks to all that responded -īut this load is 3 independent single phase supplies as the power company will not upgrade the incoming supply above 100 amp - it is rural & would involve re stringing a long distance of overhead cables to the transformer assuming this has any capacity left as it already serves several properties. The more you spread the single-phase loads across all the 3 phases + neutral the lower the sum of the current on the neutral gets. This is why you normally don't need a 'fat' neutral conductor. The latter would be the only ones actually loading the neutral, but if you distribute your various connections to 120V outlets across the 3 'live' phases and try to load them fairly evenly then they actually cancel eachother mostly out again on the neutral, so the current flow on the neutral remains small. 120V single phase between a 'leg' and the neutral 208V single phase equipment connected between 'legs' of the phases, so no neutral connection here either. Actual 3-phase equipment (much cheaper high power welding gear! ), usually does not use the neutral but uses the phase-difference between the 'legs' to operate. You'll likely have a Three Phase Four Wire Wye setup with 3 phases and a neutral in a connection using a 'star' setup. Keep in mind that the neutral in this setup is not always even used. This will be the most amps I've ever had for my shop/home in my life. They wanted $15k for the transformer to connect 3 phase.instead I decided to get a Phase Perfect for the 3 phase I'll be using. I don't think they charge me, I am only being billed $75 for the hookup as I went with 320 amps. He said he had gone out earlier but the rep had miscalculated the distance from their pole, telling him it was 60', so he took 100' of cable and was about 5' short. I just got a 320 amp service installed at my property last night, a technician called about 8:20pm to tell me he had just finished.I was surprised he was working so late, but it was still light out, surprisingly. I am not sure if neutral feeding back to the power company is based on the service or not, so will defer to someone that may know. That's an interesting thought on the neutral, I hadn't thought of that, but it seems it would need to be able to handle the amount of amps for the entire service, which changes depending on location. ![]() ![]() Hi - trying to help out doing some electrical work on a farm & could use a 2nd opinion - we have a qualified electrician on site but he is only familiar with single phase - due to change of use of some out buildings they need to run a new supply in from the incoming power supply - the power company cannot provide more than a 100 amp supply without incurring huge costs but are happy to provide 100amps per phase 3phase - most of the power will run single phase showers / lighting / cookers - the question came up what size cable is needed - the electrician looked this up & made suitable allowance for distance & I agree if the load was across the 3 lines but as each line will be loaded against neutral I made the point that logically the neutral is carrying back the total load of all 3 lines so should be of 3 times the cross section of the lines - as all SWA cables I'ver seen have equal conductor size this means the cable would need to be 3 times the theoretical size looked up - I offered the opinion that options could be use a transformer taking 3phase in & giving a single phase output of the combined line capacity which would be expensive & waste some energy - or use a 3core cable for the lines & run a separate bigger neutral - or my personal choice is not to use 1 cable but do 3 runs of concentric cable so each line has it's own cable & matching size neutral this is easier to work with & more flexible given that it will need dragging in through some wall cavities - any thoughts from the electricians out there ? I know we have several knowledgeable guys on here ( in the UK so it's 3 lots of 240 volt ) many thanks in advance for any informed opinion - I have no liabilities involved as the electrician will be signing off any work done - he's just a bit out of his experience zone on this. ![]()
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