Dual Feeder

[poni]

I dont do it myself as i don't like it, I see it a lot on large supplies and when i look and do the calcs it normally doesn't work out well, My opinion is its done by muppets who a. don't know how to do a job properly and b. don't have the kit or knowhow to do large cables

you are right, but some time's the devil drives.  

 

[Manator]

A factory I am working in at the moment want a new supply for a machine they are installing in June, we have been asked to supply 400amps to the control panel. They only require 250amp but it is expected that the ovens will be increased over time.

The run from the section board is 100m and we have decided to run a 150mm 5 core SWA cable. The cable install is going to be at least 5m away from the control cables, apart of course where it enters the panels. The cable tray work was installed over the last couple of Fridays after shut down, so we are all ready to install the cable. I will take some pictures over the next few weeks and post them when its all done and dusted.

 

[Manator]

Apparently it is my new companies policy. I have argued that the 4 core with armour is sufficient but they have always supplied SWA cables in 5 core.

I must admit I do like the idea, a little over the top but money is no object for this company so I am happy to comply :innocent

Only trouble is when testing the R1+R2 tests are lower than my multifunction tester will go to!!

I was asked to design the install in conjunction with the panel builder, I suppose my new company is testing me out. I initially specified a 4 core cable but the MD said we only do 5 core. Apart from that he is happy with my design and on close down I have 4 weeks for the install.

Now I need to pay for my CMSE hopefully in June :slap

 

[Evans Electric]

We used to do this quite often , parallel feeders ,  must be the same size & run adjacent to each other .     Seemed to do it a lot with aluminium core SWA s .  

Don't know if its been re- addressed in the latest regs  , I'm talking about the 14th & 15th edition  days.

 

[Essex1]

Megger do a decent meter for low ohms - I have one  :innocent

http://isswww.co.uk/megger-ltw425

I always use 4 core with armour and a secondary cpc myself, the larger cables are a bugger anyways without adding a 5th core  :C  But if thats what they do then who are you to complain 

We do the same. Almost 100% of the installations we do do not actually require a separate but the client likes to see it.  So you just do it. 

 

[Manator]

Megger do a decent meter for low ohms - I have one  :innocent

http://isswww.co.uk/megger-ltw425

I always use 4 core with armour and a secondary cpc myself, the larger cables are a bugger anyways without adding a 5th core  :C  But if thats what they do then who are you to complain 

I will get my company to order one, looks just right for the job.

 

[Essex1]

We are like brothers then @Essex1  :Blushing

Schucks!

 

[Manator]

Remember MM is your man  :innocent

Its a really nice meter - had mine a few years now and it will do PSC up to 40kA (The 425)

Also has some nice R1R2 memory stuff (And megger are forum sponsors as well)

Datasheet attached

View attachment 6684

I will get my boss to contact Mark and get one ordered.

 

[poni]

a bit off piste  

I was doing some testing on a cross-rail job last week they had some big motors, Star/Delta fed with 2 x 25mm 4 core SWA, the blue core was just taped up in the terminal  box with a supplementary 16mm earth run along side both SWA back the main MCP

don't know why, maybe you guy's would know why they did not connect the Blue(with green/yellow sleeve)  core to the Earth at each end?     

 

[SLIPSHOD & SLAPDASH]

We used to fit twin feeders  on a lot of BT jobs . It would of been near impossible to have got one large cable  in, let alone terminate it. These were huge cables, 100 mm 4 core at least

 

[kerching]

We Have used 400mm AWA singles doubled up from sub-station to main MCCB panel board in server rooms before now. Usually to give a 1200A/phase supply

 

[Evans Electric]

a bit off piste  

I was doing some testing on a cross-rail job last week they had some big motors, Star/Delta fed with 2 x 25mm 4 core SWA, the blue core was just taped up in the terminal  box with a supplementary 16mm earth run along side both SWA back the main MCP

don't know why, maybe you guy's would know why they did not connect the Blue(with green/yellow sleeve)  core to the Earth at each end?     

Seems stupid to me Poni, if you have a spare core within the cable why not make use of it ?  No doubt someone will have a reason for it .

Sounds as daft as one we had to do on a new build hospital .    This was way back in time but in the boiler room there was a row of 3Ph pumps , not that big as I remember . we had an isolator by each one then flexible conduit to the motor containing 3 reds & a green .

The consultants were used to seeing that flexible with an earth wire coiled on the outside so they insisted we had lables made saying " Earthwire contained inside flexible"  on every one .  

 

[Davethsparky]

To be honest I cannot recall. 

The client want 100A 3 phase for the new supply. 

I would have thought the two 50mm will be adequate for 100A over that distance. 

 

[Tony S]

One advantage of multiple feed cables is if one gets damaged you take it out of service and carry on with the other one while repairs are made or a new cable pulled in. Rather the surviving cable get warm than me being roasted for shutting a plant down longer than necessary.

As Dave said three and four paralleled cables for large boards isn’t uncommon. I can’t think of any of our main MCC’s on a single cable.

 

[Davethsparky]

Megger do a decent meter for low ohms - I have one  :innocent

http://isswww.co.uk/megger-ltw425

I always use 4 core with armour and a secondary cpc myself, the larger cables are a bugger anyways without adding a 5th core  :C  But if thats what they do then who are you to complain 

A secondary cpc? How much fault current will it actually see compared to the cable armour? Bearing in mind the armour would need to be able to handle the PFC anyway to fulfill its function. 

I've heard many arguments to say that a 'secondary cpc' is wholly unnecessary and even one person  say it is not compliant with 7671, but I'm not so sure about it myself. 

 

[Essex1]

A secondary cpc? How much fault current will it actually see compared to the cable armour? Bearing in mind the armour would need to be able to handle the PFC anyway to fulfill its function. 

I've heard many arguments to say that a 'secondary cpc' is wholly unnecessary and even one person  say it is not compliant with 7671, but I'm not so sure about it myself. 

Although you are completely correct for some reason 'engineers' who set the specifications on my schemes specify a separate cpc on almost every sub-main/circuit. 

I done a design on Amtech last week and the sub-main cpc from the switch fuse to the only DB came in at 2.5mm.  Straight away I changed it to 25mm. Just not worth the argument. They pay the invoice.  :B-

 

[Davethsparky]

There is always an argument for and against and everybody will have a different interpretation.

Yes there are many arguments in each direction, what I've been struggling to establish for quite a long time is the actual technical facts of the matter. 

Most of the arguments for an external cpc seem to revolve around non-technical reasons or flawed logic as far as I can tell. 

But the arguments against, whilst appearing to have a technical basis, seem to be lost in a bit of smoke and mirrors as people try to adjust the science to support their arguments.

i think the best conclusion that can be drawn is that it does no harm to install it (other than cost) 

 

[NozSpark]

The refs do allow for this... it's specifically mentioned in the regs ref eddy currents (sort of)

 

[Davethsparky]

The refs do allow for this... it's specifically mentioned in the regs ref eddy currents (sort of)

If you read that reg carefully you'll see it only applies where the separate cpc is required, but the argument I have heard on this is that it is not permitted elsewhere in the regulations. 

 

[DavidMartin]

Secondary CPC's or Overlays as they are commonly known are another belt and braces practice set by the DNO about 30 years ago. They weren't convinced that the steel armouring was capable of taking the fault current. There is only one cable that I've come across where this was possibly the case and that was 185 mm 3 core.