How to select the right circuit breaker for 2 mm^2 wire? - Page 1
Forum section: electronics / projects

author: Michael George
author_rank: Contributor
timestamp: July 09, 2016, 06:30:03 pm
content: I've a wire that have a cross section area of2mm2.In free air, The current rating of the wire is19 A.In Pipes, The current rating of the wire is15 A.I've installed the wire inpipesinside the walls of a room. This means I have to use an automatic circuit breaker that is less that15 A.The loads in this room are about11 Aor12 A.The available circuit breakers in shops are10 Aand16 A.If I choose the10 Abreaker to protect the wire, the breaker may trip many times per week because the loads are above10 A. The number of trips would be bothering.If I choose the16 Abreaker, the breaker will not trip too quickly but the wire may wear out because it will work above its rated current by1 A.Which breaker should I choose? I really need the breaker of 16 A.Thank you very much,

author: Ian.M
author_rank: Super Contributor
timestamp: July 09, 2016, 06:56:47 pm
content: If you overload the wire it causes insulation damage which significantly increases the risk of fire. Have you applied the temperature derating factor? Assuming an urban or desert area, it could be at an ambient temperature of up to 40 deg C which, depending on the type of wire, could reduce its rating by as much as 10%. If you need more than 10A, you should have used 2.5 mm2wire or split it into two separate 10A circuits.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 09, 2016, 07:23:12 pm
content: This depends on how the wires are installed exactly.For example, things we do no know right now, but could assume:- Solid copper wire.- PVC insulated.- Wall type.- Length.Typically, since even 1.5mm is allowed 3600 Watt(yes, 16A*)rated extension cords:- 16AB-classcircuit breaker.- 30mA RCD if it's a bathroom.But ifyour regulationssay thay you have to use a 10A MCB for 2mm. Then you have to use a 10A MCB for the insurance policy.They are allowed to not pay out if the cause of fire is determined to be a faulty installed electrical installation.*they do fail.

author: Kilrah
author_rank: Unknown
timestamp: July 09, 2016, 08:00:11 pm
content: Quote from: Michael George on July 09, 2016, 06:30:03 pmThat's going about it backwards - if you need 16A, then you need to select your wiring to safely supply 16A following your local regs. You might need to use 2.5mm2 instead (or not put everything on the same circuit).

author: Zero999
author_rank: Super Contributor
timestamp: July 09, 2016, 08:01:38 pm
content: Quote from: Jeroen3 on July 09, 2016, 07:23:12 pmThe extension lead in the picture appears to have been fully loaded, whilst completely wound. An extension cable can only be safely used at its full current rating, when fully uncoiled, otherwise there's no where for the heat to go.The ambient temperature makes a huge difference and original poster's location says Egypt which is a lot hotter than the Netherlands, so it wouldn't be surprising if the regulations require thicker cable for the same current.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 09, 2016, 10:03:21 pm
content: Yes. They are derated by 60% when wound. People often ignore this, and then you're going to have a bad day.