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Hi all, Ive been asked to supply a 110V distribution board containing 1 x 40A and 2 x 32A DP circuit breakers. The company ordering the work has provided a new 12KVA CTE transformer.
Its been a while since I did anything like this so I just wanted some opinions on whether or not I am installing correctly.

I have a primary supply of 230V from a 50A DP mcb. from that I run 16.0mm armoured to a 63A DP isolator local to the transformer. I connect LN to the primary and earth to the earth lugs and centre tap.
I then connect 25.0mm armoured to the secondary and run through a local 100A DP 60898 and into the mainswitch of my distribution board containing the DP mcbs. I also take a 25.0mm earth from the centre tap to the earth bar of my distribution board. (the earth is therefore connected from supply-transformer-centre tap-110v disboard)
If memory serves me correctly I willhave 110V between my supply cables and 55V to earth.

Does this all sound OK to you guys? Aslo, do I use 2 x brown cables for the 110v supply to dis board as neither are a neutral?
Please go easy on me, its been a while since I tackled this.

Thanks.
 
A 12500 (12000 not specified) in the tables I have is unsuitable for mcb front end protection you will find even a 63(d) will trip on the inrush you will have to redesign the supply side and choose a suitable protection device to allow the inrush which can be up to 25x 'In' so if you already have the transformer see if it has manufacturers recommendations. Does the sight have 3ph available its crazy to use this size on single phase if a 3ph option exists.
 
Yes the site has 3phase available locally but they have already purchesed the transformer. Is there any chance ill get away with it?
 
If you want single phase 110v then unless you go for a Scott connected transformer three phase won't help as at best you will end up eith L-N or phase - phase. A Scott connected transformer would distribute the load over the phases better but even then it wouldn't be balanced. It would be an expensive solution and would probably have to be made specially.
 
If you had a 3ph transformer with 3ph output you then fit a 3ph dist boad and balance the loads, I cant say whether you can get away with what you have bought as I have zero knowledge of the install what has already been purchased etc etc If its the company that's ordered the transformer who told them the spec of it... if they did the spec themselves then approach them with the pro's and cons and weigh up a costing for the single phase set up and the 3phase .... have you calculated the loading on adding this to 1ph of the supply against what the building is already using.
 
you need to look at the inrush thing a bit more - if the isolator is used frequently this could well end up quite unreliable and the type d might fail if exposed repeatedly, you might need a higher rating..... And larger cables .... Or you might find fusing a better solution
I'd really want to know what they will connect. I don't think you can select final mcb type without this knowledge.......
you also might want to run the earth for the secondary side independently so that if there is a fault in the transformer then the 110v side earth potential rise is limited ..... Oh and yes two browns or a brown and black or grey
 
Yes, the mains room is fed via an 800A submain from which we will take a new sub main. there will be two identical 12kva transformers feeding two identical distribution boards. On top of this there is a 50A SP supply to a local fuseboard which has sockets, air con, 3kva transformer, lights etc. In short there are 3 50A supplies fed from 1 new 3 phase dis board so I would put 1 X 50A SP breaker on each phase. Supply to the new board is 75m of 50mm 4 core armoured with a single 50mm earth protected by BS88 100A.
 
Thanks, we do need single phase 110v. Ill give it a go on a type D and see id it holds through start up. Does the rest of what im doing sound OK to you guys?
You can try but the primary current of a 12Kva transformer is about 52.18amps typical inrush is 10-15times FLC and its common for them to reach values of 20-25times FLC, these both exceed the inrush tolerances of type D which is typically 10-14times so to get around this you can increase the mcb rating unfortunately 63(d) mcb will only tolerate a 10Kva transformer and we have run out of the range as 63amp is the highest rating. This is why I said you need to redesign your front end protection to allow inrush. If the transformer has any manufacturers installation guide I would refer to it.
 
On each 110v board the 40A feed heating elements which are stat controlled and the 2 x 32A feed lots of controls and panels. I will call the tranny manufacturer in the morning to get some specifics on in rush.
Once they are on they will stay on basically, apart from servicing, thats the idea of having two, so only one shuts down at a time.
 
Take more care on the 110 v side too. The elements may take some time to reach temp compared to normal 230v and so initial current may be quite a bit higher than normal full load so you'll need to allow for this
dont size things too tightly.... Manufacturers should help or measure cold resistance if you have access to them.
 
Now the info is flooding in this changes the view we have of the job, you want to look into either HRC fuses or mccb's you need to review the inrush tolerances of the fuses, don't assume like most that sticking a motor rated (gm) hrc fuse in rated at 63amps is going to be large enough, check this info sheet in the first few pages it gives recommendations for fuse sizing for transformers http://stevenengineering.com/tech_support/PDFs/06IECBRFUSE.pdf you'll be supprised how large you primary fusing is required to be.
 
Thanks, the spec says the initial current will be under 40A. Although all I have been asked to do is supply 1 x 40A and 2 x 32A circuits. The connections to this will be made by controls engineers from another company. My work stops at the 110V board and I am just installing what they are asking me for.
 
You are good. Ill give it a look now. Thanks so much.
Now the info is flooding in this changes the view we have of the job, you want to look into either HRC fuses or mccb's you need to review the inrush tolerances of the fuses, don't assume like most that sticking a motor rated (gm) hrc fuse in rated at 63amps is going to be large enough, check this info sheet in the first few pages it gives recommendations for fuse sizing for transformers http://stevenengineering.com/tech_support/PDFs/06IECBRFUSE.pdf you'll be supprised how large you primary fusing is required to be.
 
You are good. Ill give it a look now. Thanks so much.
Thankyou just bored on a Wednesday night, only thing to be wary of if you choose a Switchfuse for the front end then do ask for motor rated fuses 'Gm' or it will come with 'Gg' general use, sometimes they will supply as extra's leaving the general fuses inside for your stock.
 
I have time on my side lickily. I need to power the submain and then have time to sort the tranny supplies.
I will talk to manufacturer in the morning and go from there.
Thanks again, Ill post back how I get on.
Thankyou just bored on a Wednesday night, only thing to be wary of if you choose a Switchfuse for the front end then do ask for motor rated fuses 'Gm' or it will come with 'Gg' general use, sometimes they will supply as extra's leaving the general fuses inside for your stock.
 
So this tx is used to provide power for control circuits and heaters? No tool use?

Using a CTE tx to supply control voltage to panels causes all sorts of problems fault finding when something goes wrong.
 
Its been a long time since I have tested anything 110volts fed from a transformer, but correct me if i am wrong but don't the transformer put out 55volts on both legs ? and therefore you need to double pole everything ?
 
Its been a long time since I have tested anything 110volts fed from a transformer, but correct me if i am wrong but don't the transformer put out 55volts on both legs ? and therefore you need to double pole everything ?

If it's a CT transformer. Daz
 

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