The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
Calling all Non-US members!! (Non-US only)
by Tjia1981
11/27/16 06:33 AM
New in the Gallery:
12.5A through 0.75mm² flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 15
HotLine1 10
Trumpy 8
Texas_Ranger 8
sparkyinak 7
Who's Online
1 registered (sparkyinak), 237 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#140409 - 03/02/04 08:10 AM Irish alternativ to ring mains....
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Look at this cable:
http://www.idh.ie/product_detail_guardian.htm

The cable isn't very interesting, but the ampacity tables are. According to this, 2.5 mm2 will do fine with a 32A breaker if it is clipped directly.

Top
Test Equipment:

Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement

#140410 - 03/03/04 04:01 AM Re: Irish alternativ to ring mains....
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
We can have a 2.5 sq. mm spur cable from a 30/32A ring circuit, but in that situation there will be a 13A max. fuse at the distant end.

I don't like the high ratings that are being given to cables these days. This is definitely one area where the rules have changed for the worse.

Top
#140411 - 03/03/04 04:23 AM Re: Irish alternativ to ring mains....
djk Offline
Member

Registered: 12/26/02
Posts: 1269
Loc: Ireland
That cable's aimed at both UK and Irish markets btw. (the core colours displayed on the picture are for the UK market).

Also bare in mind that there are other regulations regarding cable sizes and that the manufacturer's higher declaired ratings are not necessarily taken into consideration as they are only giving the extreme upper limits.

However, I would agree with paul there is a growing tendency to keep costs low by reducing safety margins.

That being said, the vast majority of fires caused by electrical installations here are not caused by under-rated cable. They're usually caused by by-passed / incorrect fusing in old installations where cable is either overloaded or subjected to a continious fault.

However, in general electricans don't design their installations to run at the maximum temp.s sustanable by the cable! I can't see the 2.5mm cable being used for 32A circuits under the current regs here even if in theory it could carry it it would be VERY warm.

Also their foot note:

The above current ratings are based on a ‘single circuit’ in accordance with the IEE Wiring Regulations BS7671, Table 4E2A.

Where a conductor operates at a temperature exceeding 70C it shall be ascertained that the equipment connected to the conductors is suitable for the conductor operating temperature. (BS7671 reg 512-02).

The above-tabulated current ratings should be multiplied by the rating factor (0.8) when conductor-operating temperature has not to exceed a recommended terminal temperature of 70C.
---

When designing a system using ring mains of a normal diameter with that cable at least you could be reasonably sure that if someone did manage to break the ring integrity by botching a DIY job that the cable would just run very warm rather than bursting into flames.

----

I really don't think that those tables are meant for the selection of cable for installation. They are the upper safety limits.

Unless you're planning on really cutting corners and having the electrical installation double as an underfloor / burried in plaster heating system

[This message has been edited by djk (edited 03-03-2004).]

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals