3 phase ring?

[Doomed]

At the moment have two 3 phase 16mm swa radials, each one going around the edge of a building with 16A outlets at regular interval of alternate phases.
A extension is to be built at the back of the building, with toilets (hand dryers etc) and showers in.
Would it be possible to extend the 2 existing 16mm radials to make a ring and put them both on the same breaker at the substation,or will we need to run a new feed.
Please quote reg numbers either way if possible.
Ta.

P.S. Its my bosses idea, not mine!

 

[johnboy6083]

i dont see why you cant have a 3ph ring. would be interested to see how the more experinced blokes on here work out the OCPD size ect.

 

[Paul.M]

No problem with extending the 2 x three phase radials into rings but that would mean bringing two phases back to the board as where taking a new radial to this extention may work out cheaper on parts and labour. Not my area of expertise (if you can call me that) but that is the first thing I would think of when designing this circuit.

If you do go ahead, the only regs that jump up at me is location of outlets being a certain distance apart and if not warning notice needs to be provided on the outlet.

 

[Guest123]

would be interested to see how the more experinced blokes on here work out the OCPD size ect.

By using the 0.67 rule of thumb.:stuart:

There's nothing at all wrong with a ring main of this nature, they are common place in hospitals, factories, caravan sites etc.

As with any type of ring, be it a ring main or ring final, load sharing is of paramount importance as (Iz) is less than (In).

WRT the 16A 'tap off's', how are you providing overcurrent protection them???

Also when you say 'putting them on the same breaker' what size is this breaker is it currently less than the cables (Iz), if so and you dont intend upgrading it then none of the above matters.:driving:

 

[Doomed]

The tap offs are on small 4 way boards, a RCD protecting 2 16A MCB's for the two 16A outlets.
I have only been in the substation once and can't remember the value of the existing breakers for the radials.
I think the bosses theory is that as the existing radials are so close to the new build it would be cheaper to extend them till they meet then run a new long feed.
I think he is hoping to join them in a new 3 phase DB to power the new build, and upping the main breaker in the substation to allow for more load.

 

[Knobhead]

Just regard it as any ring. There’s no mystery to it. But you do need to consider the tee off’s for the separate sub boards

The last three-phase ring I put in had a 500A CFS feeding it, it had EE Tee off boxes with type J fuses for each feed drop. It was 25 years back
View attachment 8560

 

[platty1005]

Been a spark for 37 years never heard
of a 3 phase ring for single phase circuits
Parallel sub feeders yes
11Kv substation ring yes
My advice speak to a professional designer

 

[Knobhead]

Because you’ve never heard of it doesn’t mean they don’t exist.

 

[malcolmsanford]

The tap offs are on small 4 way boards, a RCD protecting 2 16A MCB's for the two 16A outlets.
I have only been in the substation once and can't remember the value of the existing breakers for the radials.
I think the bosses theory is that as the existing radials are so close to the new build it would be cheaper to extend them till they meet then run a new long feed.
I think he is hoping to join them in a new 3 phase DB to power the new build, and upping the main breaker in the substation to allow for more load.

Well I've been doing this for 40 yrs and have installed many ring mains within an installation.

Not sure what this long feed is feeding, but don't like the idea of a ring having a long feed back if it is going to be a ring.

 

[Guest123]

The tap offs are on small 4 way boards, a RCD protecting 2 16A MCB's for the two 16A outlets.
I have only been in the substation once and can't remember the value of the existing breakers for the radials.
I think the bosses theory is that as the existing radials are so close to the new build it would be cheaper to extend them till they meet then run a new long feed.
I think he is hoping to join them in a new 3 phase DB to power the new build, and upping the main breaker in the substation to allow for more load.

I think you need to address the 'unfused' tap-off situation. Anyone could add anything to these DB's which could cause an overload situation as there is no overcurrent protection at the point of tap off.

Normal process is to terminate the ring main into a switchfuse at point of tap off and connect loads into load side thereby affording overload protection at that point.

I dont like the idea of just plonking a whole DB on this ring without using some sort of overcurrent protection, i.e using an MCB as the incommer for the DB.


Equal load sharing is key IMO.

 

[Chr!s]

At the moment have two 3 phase 16mm swa radials, each one going around the edge of a building with 16A outlets at regular interval of alternate phases.
A extension is to be built at the back of the building, with toilets (hand dryers etc) and showers in.
Would it be possible to extend the 2 existing 16mm radials to make a ring and put them both on the same breaker at the substation,or will we need to run a new feed.
Please quote reg numbers either way if possible.
Ta.

P.S. Its my bosses idea, not mine!

I can see no issue with creating a ring, whats the load on the two radials like, if they are already loaded up joining them together wont help.

Regards Chris

 

[Engineer54]

Been a spark for 37 years never heard
of a 3 phase ring for single phase circuits
Parallel sub feeders yes
11Kv substation ring yes
My advice speak to a professional designer

Pretty much standard practice in an industrial situation. so long as the Tee Offs are protected accordingly, it makes for a good general purpose power distribution system. What the OP describes for these 2 radials, it makes good sense to make them into a ring. At 16mm I doubt you would need to increase the protection device by too much either, if at all, unless VD was a major consideration on the radials...

 

[Knobhead]

That’s two of us singing from the same hymn sheet.