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Good morning All,

Ive been asked to work out the potential volt drop on 12 metres of 10mm x 7 core SWA powering a 45kW (60hp) motor.

Just to check my findings as below, please could someone confirm whether I have done it right.


45kW - 80amp FLC

as using Star Delta Starter

multiply by 0.58 = 46.4 amps

10mm x 7 core SWA has acarrying capacity of 58 amps per phase.

The voltage drop I believe is 4.0mV per metre multiply by 12 metres = 48mV which I also believe to be around 0.06 of an amp.

Best regards

Simon
 
Local isolation is always good practice where motors and plant machinery are concerned, especially on roof mounted locations. Ideally located on by (adjacent) the equipment, otherwise I've always applied my own rule of thumb, ie, never more than 3 metres distant, labeled and always within line of sight.
 
DW. The plants I worked on a central machine isolator would be a waste of time. 30m long machine? It would be 30m to the lift, down 6 floors, 30m walk to the switch room, isolate drive and go back again. Some would be get in the Land Rover, drive half a mile, isolate and drive back again. The site was 2 miles square! Every single drive, large or small had a local isolator.
 
DW. The plants I worked on a central machine isolator would be a waste of time. 30m long machine? It would be 30m to the lift, down 6 floors, 30m walk to the switch room, isolate drive and go back again. Some would be get in the Land Rover, drive half a mile, isolate and drive back again. The site was 2 miles square! Every single drive, large or small had a local isolator.

With all due respect Tony you working experience is beyond most on this forum and the examples you give are also the extreme cases re' others reading, i was generalising and did express that it was situation dependant and yes agree in your case local isolation would be a must but your on a Electricians forum not an Electrical Plant Engineering forum and if a control system operating various motors etc an be isolated and locked off then all motors etc on that system don't require local means of isolation unless it is deemed that a risk exists or in your case the bloody thing is covering 2mile square which i expressed is a situation in which i would also fit an isolator.

My original comment was aimed at someone who is relating his domestic learnings and commenting on Plant Electrical installations that although have to meet 17th with regards to the supply to them also are subject to a different st of regulations.

No disrespect here but im also prone to dragging in my out of the norm experience and pulling the rug from a general comment or question but im learning with re' to this forum that what i do day in and day out is out of the general norm of this forum and the majority are domestic and commercial basic installs which gives us easy pickings to see flaws in their reasoning or understanding of the reg's but what we point out will probably never be a situe they come across.
 
Doesn't it state in the regs that all fixed motors have to have "local isolation".. I'm sure there are lots of people who would interpret "local" differently.
 
Doesn't it state in the regs that all fixed motors have to have "local isolation".. I'm sure there are lots of people who would interpret "local" differently.

No it dosn't!... The regulation you refer to 132.15.2 and the word 'Local' is not used.
Another reg' which is relevent is regarding switching off for mechanical maintenance 537.3.1.2 which does allow remote isolation if the switching off is continuously under the control of any person performing such maintenance.

And 537.2.1.5 clearly allows remote isolation if mentioned conditions are met..... now when you start getting into Electrical control systems, Plant and machinery you may be guided by BS EN 60204 which is outside the scope of 17th but the regs above are the relevent ones for this little debate but yes i will agree with Tony if your motor is on a different floor, room or area to the control system then it would be good practice to have a local point of isolation for maintenance but this isn't always required under the 17th, if you can safely lock off the supply and you hold the the key or one of a series of keys(no copies but each one unique to that site) that need to be used unlock the isolation device then local isolation is not required.

The point Tony makes about in some industries its a requirement this is not because of the 17th and again i will agree but this forum is moulded around the current BS7671 and thats where my comments were relating to if he pulls up regulations out the scope of the 17th or even specific to certain sites or industry then hes going to make the relevance of my posts look questionable in the least and i hold alot of respect for Tony's experience and knowledge but lets try keep comments or responses within the scope of the 17th unless the point been made is relevant to make the OP or poster aware they may be stepping out of their depth.
 
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Doesn't it state in the regs that all fixed motors have to have "local isolation".. I'm sure there are lots of people who would interpret "local" differently.

Nope, and it can be a problem if somebody knocks an isolator off on an inverter driven motor when the inverter is running. Perfectly acceptable to shutdown and lock off at the MCC IMHO.
 

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