TNS and TNC-S In same building

[misssweden]

Unless both supplies are off the same mains cable then there is no guarantee they are fed from the same transformer. It obviously depends on the configuration of the network, but say for example there's a backfeed put on one of the cables due to a fault or ongoing work. That will come from whatever means is most suitable, which may not be the same Tx as it was originally fed from. 

 

[apprentice87]

Hi Misssweden,

I have a three phase supply here.. For several years, two phases were fed from one transformer, and the other, [as there was a fault in the cable the DNO could not be bothered to fix] was fed by sticking a link in the link box at the end of the street.

Would this be from a different transformer, and should i be concerned??

Once they fixed the original fault, [plus the second one which meant they now had a long dead section] they left all three links in for about a year. This was great so far as i was concerned, but they have taken all three out now...

john..

 

[misssweden]

Hi Misssweden,

I have a three phase supply here.. For several years, two phases were fed from one transformer, and the other, [as there was a fault in the cable the DNO could not be bothered to fix] was fed by sticking a link in the link box at the end of the street.

Would this be from a different transformer, and should i be concerned??

Once they fixed the original fault, [plus the second one which meant they now had a long dead section] they left all three links in for about a year. This was great so far as i was concerned, but they have taken all three out now...

john..

No you don't need to be concerned. I remember you mentioned this a while ago because you had issues with something. But the network gets altered a lot, and most people never notice (which is the point really). 

 

[apprentice87]

Hi Misssweden,

Thanks for that, glad to know that my motors are not going to self destruct. In the last few years they have dug up my street quite a few times, the mains cable must be in a terrible state. The cable itself is perfect, but it seems like every service joint is just knackered. They are cast iron boxes filled with pitch so far as i know, and it seems that they are just all rusting away and filling with water..

john..

 

[Tony S]

I was joking with one of WP’s engineers “pity you can’t fit zip fasteners to the trenches”.

Since I moved here 4 years ago they have done 7 repairs around a 4 way link box at the end of the road. The system is old, every joint and tee off is a weak point. But the only options are renew or make do and mend.

PS, I hate link boxes.

 

[apprentice87]

To be honest, i know that they just chucked the links back in the link box hole. I was thinking of putting them back in myself, and paralleling things up, as i had a much "stiffer" supply when they were in!!! Maybe not one of my better ideas..

john..!!!

 

[Tony S]

Try it, it ain’t fun even with the correct gear.

 

[Evans Electric]

I never heard of those different supplies before.   However I can't conjour up a problem TBH .   On the cert you have to put two supplies and as said , make the point that they are different .   Perhaps the network should have altered the TN-S  , who know knows ?  

Perhaps , if you are concerned , a letter to the DNO  and some advice from your scheme .

It sounds like the original design load outgrew the supply so another was added .

 

[Sidewinder]

It's similar to a summation supply really?

 

[Tony S]

Now that is where it gets complicated.

 

[misssweden]

Try it, it ain’t fun even with the correct gear.

Just line the links up properly and you're alright.  

 

[Tony S]

Just ignore the fizzing while you clamp them.

 

[misssweden]

Haha. Yep. 

It's the deep two-way linkboxes that are a pain to reach down with the test lamp that I don't like. 

 

[Tony S]

I like what they do now, use a MCCB first. If it trips don’t do it 

 

[apprentice87]

Ha ha, do not know what to say!!! MCCB a good idea though, but the links have to go in whatever i suppose.... Just check the voltage across the two halves to make sure it is close i would. Even if 200A were to flow, if the PD was only a few volts cannot see anything dramatic happening..

john..

 

[misssweden]

I like what they do now, use a MCCB first. If it trips don’t do it 

We use a fusemate. Great bit of kit. 

 

[Tony S]

I’ve seen them, not used them. The company spend money, don’t be silly. I wasn’t sorry when WP took over the LV network. The tenants weren’t happy, they had to pay the market price for their lecky.

These look interesting, there a few on trial in London.

Well they would be interesting if I could get the image to load

 

[Andy™]

We use a fusemate. Great bit of kit. 

probably cheaper to get the apprentice to do it instead

 

[Evans Electric]

We use a fusemate. Great bit of kit. 

Sweedy,   Whats a Fusemate?  And whats it for? :C

 

[misssweden]

probably cheaper to get the apprentice to do it instead

I am the apprentice!