maximum current for 2.5mm cable

macnug · 02-08-2014 06:27PM #1

Just wondering what the max amps for a 2.5mm cable, twin and earth.

02-08-2014 06:59PM

I don't know off the top of my head.
Normally protected by a 20A MCB.
Method of installation, length of run and cable type will all be factors.

What do you want to supply?

The largest fixed load typically fed from a 2.5 in a domestic installation is a 3kW immersion.

macnug · 02-08-2014 07:59PM

2011 wrote: »

I don't know off the top of my head.
Normally protected by a 20A MCB.
Method of installation, length of run and cable type will all be factors.

What do you want to supply?

The largest fixed load typically fed from a 2.5 in a domestic installation is a 3kW immersion.

Its for a hob, 6.6kw. The reason I'm asking is that it has a wiring diagram on the back of the hob for a 2.5 and would like to use a 2.5 but just want to make sure it could take it. I think the oven is about 2-3kw so I assume a 2.5 and a 13a plug would be ok for that.

Bruthal · 02-08-2014 08:01PM

It's probably up between 25 and 30 amps but varies according to how the wiring or cable is installed. They are protected by an upper limit of 20 amp mcb's.

Length of run wouldn't make a difference for the actual current carrying capacity, but does for voltage drop on appliances or machines etc.

02-08-2014 08:11PM

macnug wrote: »

Its for a hob, 6.6kw.

I think the regulation is a 4 sq. HR flex to the switch is acceptable.
I would not feed a 6.6kW load with a 2.5 T & E.
If you protect the cable with a 20A MCB it will trip every time too many rings are turned on.
Not the way to do it.

I think the oven is about 2-3kw so I assume a 2.5 and a 13a plug would be ok for that.

Feeding an oven from a 13A socket would not be considered good practice.
Eventually you may find scorch marks around the pins and eventually a melted plug.

The average kettle is a 3kW load, but it is only on for a short time.

02-08-2014 08:13PM

Time to get an electrician methinks

02-08-2014 08:14PM

Bruthal wrote: »

Length of run wouldn't make a difference for the actual current carrying capacity, but does for voltage drop on appliances or machines etc.

Correct, but I am working on the basis that this is a real life situation and the OP wants to comply with regulations

macnug · 02-08-2014 08:30PM

2011 wrote: »

I think the regulation is a 4 sq. HR flex to the switch is acceptable.
I would not feed a 6.6kW load with a 2.5 T & E.
If you protect the cable with a 20A MCB it will trip every time too many rings are turned on.
Not the way to do it.

Feeding an oven from a 13A socket would not be considered good practice.
Eventually you may find scorch marks around the pins and eventually a melted plug.

The average kettle is a 3kW load, but it is only on for a short time.

So why did the electrician leave a socket at that level then, right beside the faceplateand on the same circut, so confusing. Last time I wired a hob and oven I used a junction box with 6mm but when I saw the the socket I assume it was for the oven. The other thing I don't get is why did the hob have a wiring diagram for a 5 x 1.5 and a 3 x 2.5 if your ment to use a 4mm? By right I should get my rec to do this but I'm trying to save a few quid and I'm not a complete idiot with the right advice.

Sir Arthur Daley · 02-08-2014 08:43PM

macnug wrote: »

So why did the electrician leave a socket at that level then, right beside the faceplateand on the same circut, so confusing.

Two possible reasons, future provision for power for a gas hob (for spark). If the socket has double pole isolation from a wall switch it could be intended for under counter oven. These ovens are being supplied increasingly fitted with plugtops.

02-08-2014 08:44PM

macnug wrote: »

So why did the electrician leave a socket at that level then, right beside the faceplateand on the same circut, so confusing.

On the same circuit as what, the hob?
The hob is not normally on an RCD and sockets should be.
A socket outlet and hob should not be on the same circuit.
Besides it would not be normal to feed a 2.5kW oven from a socket.

Is the faceplate wired in a 6 sq. and fed from a 32A or 40A MCB?

The other thing I don't get is why did the hob have a wiring diagram for a 5 x 1.5

5 x 1.5 is for a 3 phase N + E

and a 3 x 2.5 if your ment to use a 4mm?

Irish regulations are for a 4 sq. HR flex.
The hob may not be made in Ireland.
A pin lug on a 4 sq. HR flex and it will fit into the connection nice and snug.

By right I should get my rec to do this but I'm trying to save a few quid and I'm not a complete idiot with the right advice.

Sure, if something goes horribly wrong it will cost a lot more.

macnug · 02-08-2014 08:56PM

Sir Arthur Daley wrote: »

Two possible reasons, future provision for power for a gas hob (for spark). If the socket has double pole isolation from a wall switch it could be intended for under counter oven. These ovens are being supplied increasingly fitted with plugtops.

Ah right didn't think of a gas hob.

macnug · 02-08-2014 09:01PM

2011 wrote: »

On the same circuit as what, the hob?
The hob is not normally on an RCD and sockets should be.
A socket outlet and hob should not be on the same circuit.
Besides it would not be normal to feed a 2.5kW oven from a socket.

Is the faceplate wired in a 6 sq. and fed from a 32A or 40A MCB?

5 x 1.5 is for a 3 phase N + E

Irish regulations are for a 4 sq. HR flex.
The hob may not be made in Ireland.
A pin lug on a 4 sq. HR flex and it will fit into the connection nice and snug.

Sure, if something goes horribly wrong it will cost a lot more.

Alright cheers for the advice, 4sq hr it is so.

06-08-2014 12:18PM

macnug wrote: »

Just wondering what the max amps for a 2.5mm cable, twin and earth.

Answer: Depends a number of factors.
Feed them into this calculator for the answer: http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

shane 007 · 07-08-2014 07:40AM

macnug wrote: »

Just wondering what the max amps for a 2.5mm cable, twin and earth.

I just looked up my "ahem" gas training manual & it has an extract from The National Rules for Electrical Installations ET101.
Table 52 F1
1.5mm CSA = Maximum 14 amps
2.5mm CSA = Maximum 18.5 amps
4mm CSA = Maximum 25 amps
6mm CSA = Maximum 32 amps
10mm CSA = Maximum 43 amps
16mm CSA = Maximum 57 amps
25mm CSA = Maximum 75 amps
35mm CSA = Maximum 92 amps

Not sure how up-to-date this table is but it gives precise parameters.

07-08-2014 08:34AM

shane 007 wrote: »

I just looked up my "ahem" gas training manual & it has an extract from The National Rules for Electrical Installations ET101.
Table 52 F1
1.5mm CSA = Maximum 14 amps
2.5mm CSA = Maximum 18.5 amps
4mm CSA = Maximum 25 amps
6mm CSA = Maximum 32 amps
10mm CSA = Maximum 43 amps
16mm CSA = Maximum 57 amps
25mm CSA = Maximum 75 amps
35mm CSA = Maximum 92 amps

Not sure how up-to-date this table is but it gives precise parameters.

It is not as simple as that.
Many variables can impact on the values provided above such as method of installation, ambient temperature and cable type.

shane 007 · 07-08-2014 08:50AM

2011 wrote: »

It is not as simple as that.
Many variables can impact on the values provided above such as method of installation, ambient temperature and cable type.

Sorry, I did not post all the text from the extract. It also states.....
"for the normal PVC insulated copper cables (ambient temp 30C & conductor temp 70C).

I would presume that the table would be a decent guide "under normal conditions". Of course if abnormal or unusual conditions were in place, then these would have to be taken into consideration.

07-08-2014 09:29AM

shane 007 wrote: »

Sorry, I did not post all the text from the extract. It also states.....
"for the normal PVC insulated copper cables (ambient temp 30C & conductor temp 70C).

I would presume that the table would be a decent guide "under normal conditions". Of course if abnormal or unusual conditions were in place, then these would have to be taken into consideration.

Some of values appear low to me.
For example in a domestic installation a 2.5mm sq. T &E is typically protected by a 20A B type MCB. However according to the values you have provided it can carry a maximum of 18.5A

I would guess that these are recommended maximum design current values, not the maximum current carrying capacity for these cables. There is a subtle difference.

shane 007 · 07-08-2014 09:54AM

2011 wrote: »

Some of values appear low to me.
For example in a domestic installation a 2.5mm sq. T &E is typically protected by a 20A B type MCB. However according to the values you have provided it can carry a maximum of 18.5A

I would guess that these are recommended maximum design current values, not the maximum current carrying capacity for these cables. There is a subtle difference.

Could be alright. As I said it was an extract from our training manual which says it's a table from ET101. The manual is quite a few years old now so the current ET101 may have an updated table.

brightspark · 07-08-2014 10:58AM

Current regs, Table A52-F1, PVC INSULATED CABLES WITH COPPER CONDUCTORS, conductor temp 70C, ambient temp 30C....

gives a range of current carrying capacities from 18.5A to 30A depending on the installation method.

So as 2011 has said there isn't a simple answer.

Edit also included table A52-F2 (but the first table does allow up to 29A)

maximum current for 2.5mm cable

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