ring main style circuit feeding residential mobile homes

[james86]

Ok, there are 3mobile homes on a 60amp 16mm radial. Tenants are complaining to site owner. He does not want to have to give them individual supplies. Could they be formed into a ring by running a 16mm from end home back to mains??? And if so what would you fuse a 16mm ring main at???? Any ideas or recommendations welcomed

 

[Paul.M]

Table 4f1a 16mm =73A. X 2 = 146A but please wait for more experienced members to confirm because I've never done a ring in 16mm and I'm sure there will be more to it than that.

 

[james86]

Could you times it by two though?? I mean 2.5 radial can be fused at 20 amps, yet we don't fuse the ring at 40?? It would have to be a hell of a supply to warrant that much ampage. Diversity would come into it I suppose. But thanks for your feedback, i would prefer individual radial myself!,lol

 

[Paul.M]

Yes, sorry James times it by 2 is not correct, take no notice of me. It also depends a lot on the type of cable and which method it has been installed.

What are the tenants complaining for?

 

[james86]

I think its voltage drop and being limited to a twenty amp supply. Not good really. Must of just started out as one home originally, I guess. Swa, underground into ip rated housing units with tails coming out of a henly through a twenty amper to the home.

 

[Paul.M]

Your idea of a ring is a cheaper way than a full rewire increasing the csa from the supply. May be an idea to fully test existing cables to confirm volt drop and flc before continuing.

 

[malcolmsanford]

James the problem would be if you just returned another 16mm from the last load point back to the DB, though you have created a Ring Main you have also created an unbalanced ring main, as there would be very little load on the return leg, and you will still have the same problem, perhaps an even greater problems as you would be increasing the protection device size, thinking that your having a balanced Ring, and the increase of load on that 16mm will give rise to temperaure on the outgoing leg cable and could result in damage.

Unfortunately because your wanting to keep a single protection device for the 3 plots you can not run a parallel cable to supplement the existing cable as you will fall foul of regulation 433.4 regarding isolation or switching within the circuit.

There are ways you can do this, create a ring main and balance out the load, but with just 3 loads that will make it difficult but not impossible, Kerchoffs law is your guide there.

If possible can you utilise a 3 phase supply ?, that way you can run a new 4 or 5 core SWA which could be smaller than the 16mm and give you a better balance.

Then of course increase the size of the 16mm to say a 25mm .

 

[Engineer54]

What sort of distances are we talking about here??

Seems your having to deal with another of those landlords that wants the rents every month but doesn't want to know too much about his tenants safety and responsibilities. Anything that can be one on the cheap is fine by him!!!

 

[Chr!s]

Ok, there are 3mobile homes on a 60amp 16mm radial. Tenants are complaining to site owner. He does not want to have to give them individual supplies. Could they be formed into a ring by running a 16mm from end home back to mains??? And if so what would you fuse a 16mm ring main at???? Any ideas or recommendations welcomed

It may well be valid, you need calculate though to see what sections carry what current assuming a greater load, and whether converting to a ring is a worthwhile expense.

 

[SirKit Breaker]

Threaten to take the lot out and let them go back to Calor gas, mantle lighting, no telly, and a 15 minute treck to the toilet block across boggy fields in the rain for a shower I bet that will stop them whinging

Cheers........Howard

 

[Guest123]

The general rule of thumb for ring mains and their OCPD's is to multiply the OCPD rating by 0.67, i.e a 100A OCPD x 0.67 = a cable with a minimum CCC of 67A with any factors applied for the ring main.

Whats more important though is to ensure the loading is equally distributed thorughout the ring main as much as possible.

 

[Sintra]

Balancing the ring would be the problem. What you would need to do is have the last property as the centre point of the ring. So to do that you would need to go from the db to property 1 then link property 1 to property 3. Then returning from property 3 to property 2 and back to the db from property 2.


Sent from my iPhone using Tapatalk.

 

[Chr!s]

Balancing the ring would be the problem. What you would need to do is have the last property as the centre point of the ring. So to do that you would need to go from the db to property 1 then link property 1 to property 3. Then returning from property 3 to property 2 and back to the db from property 2.

The ring does not need to be balanced, you would need to calculate the distributed current to see if its a worthwhile exercise.

 

[Engineer54]

The ring does not need to be balanced, you would need to calculate the distributed current to see if its a worthwhile exercise.

It could make a difference if the original leg of this proposed ring is substantially shorter than the new leg or vise versa. The majority of the load will then tend to pass along the shorter leg of the ring.

Another possible solution, is to provide a parrallel cable with existing cable to a central W/P DB , and supply the Three residential moblie homes via short protected radials...

 

[BillyTheSparks]

could you not just run a seperate 16mm swa to the last home (depending on distance etc), and disconnect it from the first and second ones?
so the outcome being the third plot on it's own radial, and plots one and two on their own radial??

 

[james86]

Hi guys, sorry late getting back to you.....interesting points have been put across. The distance from the 1st home to mains is approx 45 metres and then from the end home about 65 metres. Rather than bury the SWA i think he must just have a speed bump in the park rd built on top of the SWA cos theres lots of speed bumps!!!

 

[Chr!s]

It could make a difference if the original leg of this proposed ring is substantially shorter than the new leg or vise versa. The majority of the load will then tend to pass along the shorter leg of the ring.

Another possible solution, is to provide a parrallel cable with existing cable to a central W/P DB , and supply the Three residential moblie homes via short protected radials...

This is my point, you wont know until he calculates as to what benefit will be gained. A lot will depend upon what the clients require.