Connecting up Sockets in either office or home

Hi,

It all sounds a bit sketchy to me. Is this a building site or fabrication works?

How much load is already on the 2 transformers?

Well with it being a fabrication works the Welding machine maximum Power is 16kW there are two power cabinets on each side. I guess your going to say that the transformers need to be bigger?.

Normally we assume that 13A sockets  are not all fully loaded at once, and base the sums on floor area for general  use or known maximum demand if there are specific figures available.

Office or home is not normally that heavily loaded, as you cannot cool a large area indoors that fast - say 32A for as many sockets as you like in 100 square metres. 4mm if radially wired 2.5mmsq if a ring.

It is not clear where the welders and transformers fit in - are these normal 13 Amp sockets, or are they transformer isolated ? If the sockets are supplied by the transformers, then the upper limit is 4KVA for the whole lot then you can wire it all in 2.5mm and fuse at 16A.

What are the 13A sockets intended to supply? (hopefully not the 4kVA transformers....)

   - Andy.

Also lighting may well be on a 6A breaker, being the smallest common size, but equally if there is a lot of it, there could equally be 10A or even 16A lighting circuits in some cases, and cable used may be 1mm, 1.5mm or 2.5mm, or even heavier sizes if the runs are very long and voltage drop is an issue.

Equally if the load does not amount to a row of beans (and with LED fittings this is often the case) then the cable may be thinner and the length of cable run longer than you may expect based on older systems.


As an initial rule of thumb, a cable run of 100m or more is 'long'  in that sense, and really you need to start to calculate the voltage drop properly, rather than just simply look up the current rating of the cables, when the bulk of the load is going to be around 50m or more from the incoming supply - of course it all depends on the building layout, and exactly how the load is distributed along the circuit etc - a cable with all the load at the far end is the worst case but to avoid over-sizing  or under-sizing the design, there is  no substitute for a tape measure and then a calculator.

OP tells me:

 

the sockets are there for the workbenches that are in the office so for probably soldering or general use (ie Radio etc).But in regards the transformers I believe these may need to be increased in size to cater for the Welding Machinery has the Welding machines require an output of 16KW and the 4KVA Transformers aren't big enough in output requirements.

As the sockets are for general 'small power' use, there'll likely be lot of diversity, so a large number of socket on a 32A or 20A circuit may be quite feasible, as Mike said. If you had a lot of high earth leakage equipment (like an office full of PCs) then you might want to split things down to keep the leakage on each 30mA RCD manageable (9mA max is recommended), but you could still have several sockets on each circuit.


I'm not quite following what purpose the transformers are serving (other than providing 110V RLV) - do you not have a normal 230/400V 3-phase supply? I would have expected 230V or 400V equipment, especially large loads like welders, to be connected direct rather than via a transformer (especially a relatively small one like this). As you're using "ordinary" industrial sockets (with PE contacts) I take it you're not trying to create a separated system for safety reasons.


As for the 16mm² cable on the supply side - that rather depends on what it's connected to and what overcurrrent protection it has.


    - Andy.

Jimmy - you seem to be posting replies as comments to my profile - which means only I see them (unless I copy them into my own replies) - you might be better posting them as conventional replies to this thread (e.g. using one the "Reply" buttons below each post) - that way everyone else can help too and my in-box doesn't get filled up!


Anyhow, Jimmy said:

Yeah, there are 5 large power cables (L1,L2,L3 N & E) these being 3-phases coming into the First Power Cubicle I assume these cables are connected via the transformers which at the moment stand at 4KVA each but believe cause the Welding Machinery will generate a required output of 16KW then we will need possibily 20KVA Transformer if not bigger because there maybe two welding kits of machinery wired plugged into one cabinet has there are two sockets for 400v supply.I assume these 5 cables daisy chain through to the next Power Cubicle on the first floor then the next on the 2nd and so on.And from the Ground Floor Office I was looking at connecting a 16mm2 cable from the Power Soucre Cabinet for the office via the safety distribution boards to the sockets.

  and

To light up 12 lights at once with one switch would this configuration be good enough.See attached

(unfortunately I don't seem to have the attachment)


Others here will have more experience of this kind of thing than me, but I am wondering if these 'transformers' are really more like distribution assemblies (like the ones for construction sites perhaps) - maybe with a small transformer for just the 110V sockets - rather than just simple transformers per se.


   - Andy.

Jimmy says:

 

I'm getting a better understanding of the transformers requirements they are for 110v only and the Welding Machinery just plugs directly into the 400v TP+N+E Socket that is on the Power Cubicle I was told they call these Power Cubicles are Power Cluster Units.

Hi Dennis Thanks a lot for the advice on the distribution board set up for the office. You see at the moment we don't have a power feed going to the sockets and was thinking that between the floor levels of Ground Level where the office is and the first floor there is a Main Ring Cables that connect to the transformers on the power source cabinets that contain the different sockets of 110v,230v & 400v for the different applications of output requirements (ie Welding Machines (16KW),Grinders etc).Now to power the sockets could we run a 16mm2 Cable from the inside of the Power Cabinet to the distribution box in the office (ie via 63A RCD and DP MCB and 32A MCB for the 2.5mm2 Cable to connect to the sockets now I know there are capacity requirements when connecting up sockets but can you connect say 6 13A Sockets from one 32A MCB).Lighting circuit we are looking at having one switch to operate 12 26W Strip Lights would that be feasible?.Jimmy

Thank Jimmy2Rivers for your recent reply. However it came into my profile, not the main forum, so only I saw it. Was this intentional or a mistake?


To reply to the forum, either click on the "reply" button to reply to the whole topic, or the "Quote" button to reply to one post in particular. If that post is long, preferably abridge it in your reply, to highlight the key point, or else the whole thing becomes tediously repetitive.


If you click on someone's name, you go into their profile. If you reply there, nobody else sees it on the main forum. I would ask that you only do this if you want to send someone a private message not intended for general observation. Normally it is best to share posts with others, who will see things from different angles and may come up with ideas that we do not think of.


Anyway, to answer your points:


It should be OK to run a 16 sq mm cable from the power cabinet to the distribution box. From there a 32 A MCB can serve the sockets using 2·5 sq mm cable. Wire these as a ring main. You can certainly have six sockets; in fact you can have an unlimited number if the area served does not exceed 100 sq metres.


I presume the lights are LED linear strip. I don't see a technical problem in running them all off one switch. I would think again if just one switch is the best way. Lights are often arranged in separately switched groups, so that one can switch on only the groups actually needed, in consideration of areas occupied and daylight from windows.

Jimmy said (via a comment on my profile):

So going back to the Power Clusters themselves now there are 5 cables (L1,L2,L3,N & E) I assume from the substation to the back of the Power Cluster to give it power. What would be a typical size for these cables?

It's difficult to say without knowing what's upstream - I doubt it's direct from the DNO's substation. It sounds like you've got single core cables, with perhaps single pole connectors - if so these can be rated anything up to several hundreds of amps (I'm thinking on the types usually used on temporary events installations). So I wouldn't like to hazard a guess really.


   - Andy.