# Outbuilding circuit tripping breaker

#### Davy61

Hi I took my electric from my concrete shed I don't use via it's SWA so I ran the SWA to an outside junction box then connected a 6mm wire in through the shed to the consumer British Fortress CU from there I ran a 6mm wire via the 32 amp breaker to sockets ( 3 double) I can use my pillar drill that's OK but when I used my chop saw or compressor it trips the hose breaker please help I am a DIYer but want to fix as I know it must be something simple to fix. All metal sockets in shed and all got fly earth to casing too.

#### ericmark

Size and type of breaker please,
it could be earth leakage with an RCBO or RCD, or overload with RCBO or MCB. It may be the inrush with chop saw or compressor specially the latter. You may need a different tripping curve, we have B, C, and D which equals 3-5, 5-10, and 10-20 but before changing need to know the loop impedance.

Also the RCD comes as types, AC, A, F, B mainly to do with DC and frequency, need more details.

#### Davy61

My breaker 32 amp is a B type

#### Davy61

My breaker in the shed for sockets is a B 32 amp and my CU is a British Fortress

#### Davy61

Sorry I am a novice but what do you mean loop impedence?

#### ericmark

I assume hose breaker is house breaker, so that should be larger than 32 amp as no point having a B32 in shed if house 32 amp or less.

The idea is the breaker trips with a fault, and with a short circuit very fast, so a B32 needs 5 x 32 amp to trip, it does not matter if call prospective short circuit current which must be over 160 amp or 230/160 = 1.44 ohms loop impedance, we need to use cable which will allow automatic disconnection within the prescribed time.

Note:- called resistance with DC and impedance with AC.

Sone times it is hard to get a diffrence between MCB's caravans for example, where supply is 16 amp, and 15 amp MCB's are like hens teeth. So either a 10 and 6 amp MCB or feed the 6 amp from the 16 amp, which means overload on a power circuit can stop lights working, however often battery lights.

The point is electric installations are designed, not thrown together, we look at what the cable can take without damage, but also look at volt drop and automatic disconnection times.

#### Davy61

This is inside my CU

#### Attachments

• IMG_20220530_163324.jpg
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#### Davy61

Top cable for lights bottom right for sockets and bottom left for power coming in

#### Davy61

Glands to put on when prob fixed

#### ericmark

This is inside my CU
The picture does not seem to show 6 mm² cable able to take 32 amp or any doubling up and conductors in parallel. Electric circuits are designed not thrown together, so we know the pair of MCB's limits the current to 38 amps, we know using a type AC RCD, and to get within the current rating the supply cable must be 6 mm² or more.

Using my program I have worked out needs to have no more than 26 meters of supply cable, other wise volt drop is exceeded, and when I measure with the loop impedance meter between line and neutral I expect to see around 0.58 Ω or a PSCC of around 400 amp, since a B32 MCB needs 1.365625 Ω and a C32 0.682813 Ω then seems limiting factor is volt drop.

You say you have used 6 mm² although the picture does not seem to show that, and it would need to be supplied from a 40 amp MCB in the house which you have not confirmed, you have said you have a compressor, but not said what the in-rush is for it.

To start any electric motor takes more current than to run the motor, so we use multiple methods to limit the current draw, these extend the start time, which with a compressor is often critical, as we want it to move into run mode before it starts compressing air, so the starter is often linked to a de-load valve of some sort, it means using an inverter to reduce the start load is not as easy as with other items like pillar drill or chop saw.

One of the problems with an existing supply is to ensure it has a thick enough cable for the whole of the run, I have seen new builds with garages using 2.5 mm² in the house and 4 mm² through the garden, it was on a B16 MCB so complied, but you could not have uprated to a 32 amp. And also it was right on the edge as far as volt drop goes.

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#### Taylortwocities

@Davy61 two questions
The breaker in the house that trips, how many amps is that/ What type B16, C32????

If you use a smaller load in the outbuilding, like a light, does the breaker in the house still trip?

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