Cable type for supplying 3 phase board

[Hellmooth]

Hi, I need to supply a new 3 phase DB from mains, the board will be supplying a couple of transformers which will be used for some machinery, it is in an office/unit style environment, was looking for some ideas with regards to how to run the cables, haven't done calcs yet but would be looking at 25mm supply to board, the machines draw roughly 40 amps and 2 at 16-20 amps. I was thinking of SWA on cable tray from the board to trannies and machinery, but for the supply cable would trunking and tails be more suitable? I will need to stick in a switch fuse for the tails as its is about 6 metres. Any info appreciated. Cheers.

 

[Darkwood]

Be careful here, your TX supplies will need designing with care and accounted for with the overall design, without any details its hard to say if running the machines off mcb's is even suitable, a full machine spec' is needed, its not just about the full load current as inrush is also a key factor, also if these machines have motors on them then this may also need to be factored in.


At 6m you will need front end fusing, how to install and what type of cable is all down to the environment you are in... we have very little to go on here.

 

[Hellmooth]

Be careful here, your TX supplies will need designing with care and accounted for with the overall design, without any details its hard to say if running the machines off mcb's is even suitable, a full machine spec' is needed, its not just about the full load current as inrush is also a key factor, also if these machines have motors on them then this may also need to be factored in.


At 6m you will need front end fusing, how to install and what type of cable is all down to the environment you are in... we have very little to go on here.

The transformers are 400v-480v and 400v-208v, they are for American machinery, the machines are used for making semi conductor parts. The customer requires a supply for these with isolation, then onto 63a commando sockets at the machines. I have asked about inrush details and additional info I may need. The environment is a unit/office, it is split into where the machinery is which is open space, and the offices. The ceilings are only about 3-4 metres high with wooden joists, the walls are plasterboard, any form of cable could be used without real restrictions.

 

[Pete999]

The transformers are 400v-480v and 400v-208v, they are for American machinery, the machines are used for making semi conductor parts. The customer requires a supply for these with isolation, then onto 63a commando sockets at the machines. I have asked about inrush details and additional info I may need. The environment is a unit/office, it is split into where the machinery is which is open space, and the offices. The ceilings are only about 3-4 metres high with wooden joists, the walls are plasterboard, any form of cable could be used without real restrictions.

Any thoughts about the UK/US frequency difference?

 

[Darkwood]

The KVA rating of the TX would be a good start to see what if possible MCB rating is needed and type, you may struggle trying to get inrush details, the inrush on these TX's may be what determine your whole install so if we have ratings we can probably work it out, its not as most believe as simple as a type D for TX's.

 

[Hellmooth]

The KVA rating of the TX would be a good start to see what if possible MCB rating is needed and type, you may struggle trying to get inrush details, the inrush on these TX's may be what determine your whole install so if we have ratings we can probably work it out, its not as most believe as simple as a type D for TX's.

They are 30KVA.

 

[Hellmooth]

Any thoughts about the UK/US frequency difference?

They run 50/60Hz so no issues, the guy who deals with it has more knowledge in his pinky than I have in my whole body, the machines have been moved from another site where they were used without any issues, I was more looking for opinions on what cable to use.

 

[Pete999]

They run 50/60Hz so no issues, the guy who deals with it has more knowledge in his pinky than I have in my whole body, the machines have been moved from another site where they were used without any issues, I was more looking for opinions on what cable to use.

Thanks, it was just a thought.

 

[Hellmooth]

The system supplies power to two pumps, when these start up you get an initial surge of about 15A. Other than that there is no inductive loads, its just all single phase controllers.
There will be some earth leakage especially when we initially ignite the plasma.




My idea for the best layout would be an 80/90 A MCB on the main board. This would supply:


1 x 60 for the 415V to 480V transformer
1 x 60 for the 415V to 208V transformer
(Only one of the above will be on at any one time.)
1 x 16 for the air compressor
These 3 should be on a board above the transformers in the small room.


2 x 30 on the OUTPUT of the 415V to 480V transformer going to two commando connectors mounted on other side of the wall from the transformer room and the same again from the output of the 415V to 208V transformer.

This is most recent email from customer.

 

[Darkwood]

They are 30KVA.

I wouldn't be looking at running such a size off an MCB normally, you may get away with a 63amp(D) TP mcb but dependent on the type of TX may still make this a problem, to guarantee no nuisance fusing you may be looking at possibly sw/fusing with BS88 or appropriate MCCB's for said KVA inrush, it can slightly vary with manufacturer of OCPD so double check with tech help before commiting to design... if you go for the 63a(D) then Zs compliance becomes an uphill struggle to achieve.

You may be lucky in asking how the previous company supplied them but be careful of your inexperience here as you may not recognise if the original was compliant without going into test the set-up.

Note here your TX's will need appropriate over current protection and you would be wise to look up the calcs needed to choose correctly as its not as simple as looking at the rating plate.

 

[davesparks]

I can't remember what they are called, but there is another type of mcb other than b,c,d which is designed for transformer protection. I know Schneider make them but expect other manufacturers do too.


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[joel89]

i'd use 35mm SWA on a 125a 3phase Sub DB.

 

[Pete999]

I can't remember what they are called, but there is another type of mcb other than b,c,d which is designed for transformer protection. I know Schneider make them but expect other manufacturers do too.


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Would that be an "Over current Relay? , Instantaneous,Definite Time or Inverse time relays.

 

[davesparks]

Would that be an "Over current Relay? , Instantaneous,Definite Time or Inverse time relays.

Actually what I was thinking of is the K type mcb

 

[Hellmooth]

Spoke to the supplier of the transformers and they stated that a type C or D would be fine, preferably a D but a C would manage.

 

[davesparks]

Spoke to the supplier of the transformers and they stated that a type C or D would be fine, preferably a D but a C would manage.

That's a nice definite confirmation in writing which you can use to back up your design decisions!

 

[Hellmooth]

That's a nice definite confirmation in writing which you can use to back up your design decisions!

It's cool I recorded the conversation, also looked into the laws related to recording phone conversations, think I might be alright in the court house...........but as back up I'm driving down to London to meet the guy and get him to sign a declaration of conformity, meeting a lawyer there as well he's going to record the whole meeting, all for £5k, bargain if you ask me.

 

[davesparks]

It's cool I recorded the conversation, also looked into the laws related to recording phone conversations, think I might be alright in the court house...........but as back up I'm driving down to London to meet the guy and get him to sign a declaration of conformity, meeting a lawyer there as well he's going to record the whole meeting, all for £5k, bargain if you ask me.

You can take the pee all you like, but who is going to be carrying the can if nuisance tripping occurs and interrupts this business?

 

[Hellmooth]

You can take the pee all you like, but who is going to be carrying the can if nuisance tripping occurs and interrupts this business?

You? Night Dave