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Hi All
New member on this forum 1st post
i need some good sound advice please I am a maintenance electrician and I have been asked to quote for a 3 phase and neutral electrical supply at 125amps per phase for a chiller unit that is to be hired ,to be totally honest I am out of my depth . My supervisor is non technical , I told him to get a company that specialises in this type of installation and to be fair on him that’s what he wants to do but he needs to justify using a sub-contractor
The advice I need is when designing the installation what other factors should I consider
I know the length of run and routing are the obvious ones my cable of choice would be swa xple rated at 90oC the cable run I have been told is between 50 and 70 mtrs
In my opinion the other points are
starting currents
I have yet to receive information on the chiller yet but can I assume because of the current load it will be star delta start
electrical noise I imagine it will have filters fitted
4 core cable with separate cpc or 5 core with the cpc the same size as the phase conductor
I am not sure at what size of swa that the armour cannot be used as a cpc
PFC to be taken into consideration

my user name is Dimspark if a forum member reads the above they will probably think my user name is apt
Thanks to all Dimspark
 
Firstly that's a big chiller at 125a per phase, is this a Water chiller?
It'll unlikely to be plain Star Delta nowadays, it'll be Variable speed drive which also gives soft start and also staged start up for each compressor.
Checking requirements with the supplier will still be needed to confirm the above.
Is there enough spare capacity in the existing supply to the building?

The Supervisor shouldn't need justification for using a company that is qualified and experienced in this type of installation.
Does your company's own insurance cover them for electrical installation if anything goes wrong?
The best justification is if you get the design wrong it could end up costing the company far more that the cost of using a suitable company for the job.
 
The hire company should be able to provide you with a supply spec.
It should include recommendation for breaker curve.
Normally with cables of that size, armour will suffice as cpc but you might need to consider bonding of pipework also.

Chillers of that size, the ones I have seen anyway have 3 or 4 compressors that are started in sequence to control the cooling load and therefore starting currents are not normally an issue for supply cables.
 
I know the length of run and routing are the obvious ones my cable of choice would be swa xple rated at 90oC the cable run I have been told is between 50 and 70 mtrs

Just for info: 90°C cable is only suitable for connection to items that are rated for 90°C.
Check out reg 512.1.5 (page 128 BBB). You will have to check this with the manufacturer of the chiller unit and also at your end, whatever protective device you are wiring to.

If the chiller is being hired, does it come with a 125A power connector or does it need hard wiring?
Is there any signal feedback that need monitoring?
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Another thing to consider is, depending on where this is being used, eg. its for a line of machines that has a Global Stop, then does the chiller need wiring to this stop?
 
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As already mentioned, running at 90C limit has issues with what it is terminated in, but I suspect that if you are looking at 50-70m length then the voltage drop will require a bigger cable than the 90C thermal limit anyway.

Check the CPC requirements as you might need to run a separate 16mm CPC if the armour fails to meet either the disconnection time or adiabatic limits (that would be cheaper then going an extra core in the SWA if it is mechanically acceptable).
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Actually a quick on-line calculator suggest 50mm for 90C and 70mm for 70C at both lengths for 125A three-phase in a duct, so volt drop is not dominating it yet.
 
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Go with five core, you're not paying and the higher the costs you put together the more likely a competative quote from contractors will look. Another good trick is to spec all the parts off the RS website without being logged in, the prices for some stuff on there is astronomical before discount.
 

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