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Anonymous Poster #1

400V Heater Connection

11/25/2018 10:39 AM

I have 18 heaters of 2 kw each. Rating 415V. How do I use 3 phase power to connect the heaters in best possible way? What minimum MCB rating and cable size do I need? 3 phase supply in my country is 415V, 50Hz.

Any help would be appreciated.
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SolarEagle
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#1

Re: 400V heater connection

11/25/2018 11:15 AM

18 heaters X 2 kw = 36kw / 415V = 86.75 Amps / 3Ø = 29 amps per leg...#8 copper stranded wire(or 10mm2 ) on 40amp 3Ø breaker

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67model
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#2
In reply to #1

Re: 400V heater connection

11/25/2018 1:31 PM

Pardon my correction, but it's...

18 x 2000 = 36000watts then 36000watts/(415volts x √3) = 50.0 amps per line.

Check : 50 amps x 240 volts x 3 = 36061; assuming a usual 415V, 50Hz, 3 phase & neutral supply N.B. 415/√3 = 240 volts.

A "3 wire" connection L1, L2, L3 - with 6 heaters wired L1 to L2; 6 wired L2 to L3 & 6 wired L3 to L1 - a "Delta" or "triangle" is sufficient.

How the cabling is done depends on where each heater is physically and whether they are all turned on/off together. If you have sub-circuits with fuses or breakers you will not lose all heat at once.

Each heater takes 2000/415V = 4.8 amps, which means 28.9 amps per set of six fed by two wires.

If you fed them in threes [15 amp each set of three] & they were like normal domestic room heaters, common 1.5 mm2 copper cable PVC insulated is adequate for 16 amp rating in conduit, surface mounted on internal wall at 30 Celsius ambient [only two wires/one twin cable in conduit]. There are benefits to smaller wires - 10 mm2 has hardly more than 3 times the current rating of 1mm2 & copper is expensive.

The heater may not be certified for safety in a 50 amp circuit - fusing at e.g. 15 amp may be in maker's requirement

But there are lots of regulations [starting with - each cable, as installed, must be protected against overload & short circuit to prevent fire] - e.g. if cables/conduits are buried in a wall so, not knowing location, someone could drive a nail into them then the conduit must be metal, able to carry the fault current with limited voltage rise or else there must be quick-acting earth fault protection.

This is just basic principles - you need to comply with your local electrical regulations & where I live you would have to be a registered electrician to add a 230V circuit to a home.
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khelectrical
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#4
In reply to #2

Re: 400V heater connection

11/26/2018 6:17 AM

67Model, It seems as if your answer is a phase to neutral equation. I would agree with SolarEagle that the calculation would be for 415 volt or am I missing something here.

Thanks!
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67model
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#5
In reply to #4

Re: 400V heater connection

11/26/2018 9:16 AM

My first calculation is 3 phase 3 wire 415V - the second supposing 3 wires at 240 to earth/neutral, 50 amps each is just a cross-check for those unfamiliar with 3 phase (which I often do myself, to make sure I am not "outside the ball park").

3 wire 415V line-to line, floating without neutral source would be unusual. 415V/50Hz systems are usually 415V/240V grounded Y transformer sources, 240V to neutral . (Actually, Europe has now standardised on 400/230V & here, which used to be 240V, is 230)

Best to check by a different method - even Solar Eagle was hasty & left out √3!
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khelectrical
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#6
In reply to #5

Re: 400V heater connection

11/27/2018 1:02 PM

Thanks 67
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67model
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#7
In reply to #2

Re: 400V heater connection

11/28/2018 6:45 AM

To help Original Post, assuming ambient & 3 live wires [+ earth wire same mm2 copper] PVC cable in conduit as post #2....keeping loads balanced for 3 phase.

  1. If you need long run from incomer - 63 amp fuse/3 pole MCB with 3 wires 16 mm2 copper.
  2. Sub board with 2 x 3 pole 32 amp fuse/3 pole MCB & 6 mm2 copper wire out.
  3. Each 32A breaker feeding 3 x 10 amp 3 pole MCB with 1 mm2 copper wires out.
  4. Each final circuit 1 mm2 copper using junction boxes to connect 3 heaters in "delta".
  5. If the final heaters are heating water/oil, high temperature tails connecting to junction box for PVC wires are necessary.
  6. According to temperature control needs, 3 pole MCBs can be followed by contactors with thermostat switch control.

Multi-core cables [armoured?] clipped to wall may be easier than conduit but it depends on possibility of mechanical damage/ access by unskilled persons/local regulations/practice.
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PWSlack
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#3

Re: 400V Heater Connection

11/26/2018 5:12 AM

Where is the installation instructions document for these heaters? What did the equipment manufacturer say in response to the telephone call to its Technical Helpline? What does the local, qualified Electrician have to say on the subject?

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