He was looking for guidance I suppose.A mate of mine used a pair of compasses - seriously! I wonder what their current rating is
He was looking for guidance I suppose.A mate of mine used a pair of compasses - seriously! I wonder what their current rating is
Do you have any view on a B curve 16A RCBO in the distribution board?Well, if we're going to continue down the thread resurrection patch ( ) I feel duty bound to say that it's not the 13A fuse in the plug that will make the difference, rather than the C curve C16 MCB in the distribution board...
Sure.Do you have any view on a B curve 16A RCBO in the distribution board?
Oh wow I wasn't expecting such a reply, so written well.Sure.
All MCBs (or RCBOs) will trip when the current exceeds the maximum rated current, as you would expect. However, it's not a binary "Exceed current = trip, don't exceed = don't trip" decision.
The breakers operate on a curve where they will tolerate an increased rate of current ("inrush") for a pre-determined period of time.
Inrush is dependent on how much of an inductive load is present where, simplistically put, an inductive load is something with a moving part like a washing machine, lathe, drill or compressor. Or welder...
A device that has an inductive load can demand an inrush of 2x, 5x or even 10x its normal running current. So a 3HP motor on a lathe or a drill will draw 10A once it's up and running but might need 6x that (i.e. 60A) to get going.
This is why a "perfect MCB" that just cut off at its rated value wouldn't be much use in real life.
In reality, MCBs have rating curves as per this article (and many others).
Here you'll see that a typical-household B curve MCB is has a curve that says it will (simplistically) withstand up to 5 times its rated current for up to ten seconds.
If we go back to our 3HP motor, that would suggest that we need an MCB that can handle the 16A in a ring main, so in theory a B curve B16 would do fine -
View attachment 446255
But spot the range, which is 3 to 5 x rated current. The MCB would have to sustain 60A+ for up to ten seconds, which on paper seems doable. But note the curve is 3-5 times so the minimum they will design to is 48A and, rest assured, nobody wants to go to court to defend why their MCB design hoped for the best....
Then we look at the C curve, which looks like this:
View attachment 446257
And now we have a minimum of 5 x 16A (on a C16) = 80A up to 160A. Admittedly for a maximum of one second, and then there is a rapid turn down in the current limit before it will trip.
So generally, for a tool with a high inductive load, such as a motor or a welder, you would want to pick a C curve MCB.
But (final but!), MCBs work in conjunction with a residual current leakage device like an RCD or RCBO. These devices detect leakage to earth and are what stands between you and a fatal electric shock.
To detect the leakage they must have a relatively low circuit impedance, which needs to be tested by a competent engineer with calibrated equipment. You can't just go fit a C curve (or D curve!) MCB on a circuit made up of wet string and some spaghetti strands. So before swapping a B curve MCB for anything else please do ensure that you have a competent person check the impedance of the circuit.
Oh wow I wasn't expecting such a reply, so written well.
Hand on heart, I didn't understand everything but did get the jist of what you were saying.
By question was mainly to do with safely running a small portable stick welder off a 13a plug/socket and a 32a RCBO final ring circuit.
My board is a plastic one, 10 fuses I think and has the same brand mixture of MCBs and RCBOs all B curve, that much I can remember till I can get under the stairs again to look.
I know there are concerns about plastic CU boards under a stairs but the whole of under stairs as been double fire boarded at some time, don't know if that puts me in or outside current regs?
I've been doing some reading, out of interest what's the difference between a FE RCBO and a AFDD RCBO?
I may be wrong but I'm sure I have seen some RCBOs described as a FE RCBO, some with, some without a white wire and AFDDs all of them with a white wire?
I've been doing some reading, out of interest what's the difference between a FE RCBO and a AFDD RCBO?
I may be wrong but I'm sure I have seen some RCBOs described as a FE RCBO, some with, some without a white wire and AFDDs all of them with a white wire?
That's exactly what I have in the garage. B32 RCBO in the distribution board, ring final in 2.5sq.mm, decent quality 13A sockets.By question was mainly to do with safely running a small portable stick welder off a 13a plug/socket and a 32a RCBO final ring circuit.
Thanks and I will, just nice to have some info.You'll be fine running the welder off a 13A plug and 32A ring, until you're not. In other words, push it until it trips the breaker then don't push that hard in the future!
If you have a garage or outside socket it's worth getting a spark in to check whether it's safe to put a C16 or C32 in for it.
Re regulations, a board that was compliant to an earlier version of the regs is still compliant. Requirements for new installations don't get applied to existing installations.
As for the types of RCBO I'm afraid this is where my enthusiastic amateur level of knowledge runs into a tree! @Jack Ryan or someone else can probably help us both on that
That does make sense and I hadn't thought about it that way.If you oversize the welder somewhat, every component, lead, clamp etc will be a bit beefier and loose fewer volts at your potential maximum power. A 150 welder run at full beans will blow a fuse (and overheat quicker) than a 180A run at 150, if that makes sense.
I'd consider putting in a dedicated 32A socket for it though, so your limit is not a 13Afuse but the supply and cabling and your machine.
Thanks.That's exactly what I have in the garage. B32 RCBO in the distribution board, ring final in 2.5sq.mm, decent quality 13A sockets.
I've run my old SIP Migmate 150 up to full power, and my "Static Arc" stick welder at up to 135A. Maybe "Chinese Amps" so let's say enough power to run 3.25mm rods.
If I start having trouble I would install a dedicated circuit but I'm not in a rush as I may be relocating or reworking the workshop anyway.
There are blue three pin plugs/sockets in both 16A and 32A. Also in yellow intended for 110V. Four or five pin would normally be for three phase.As above in my last post, I thought 32a plug and socket were 5 pin and the blue stuf was 16a 3 pin but could be well wrong.
Just as another opinion, R-Tech who seem well regarded on here say you can understand their MIG at up to 160A from a 13A socket.I've run my old SIP Migmate 150 up to full power, and my "Static Arc" stick welder at up to 135A. Maybe "Chinese Amps" so let's say enough power to run 3.25mm rods.
Does it start speaking Chinese over 160amp?Just as another opinion, R-Tech who seem well regarded on here say you can understand their MIG at up to 160A from a 13A socket.
Thanks, 3 phase, forgotten about that.There are blue three pin plugs/sockets in both 16A and 32A. Also in yellow intended for 110V. Four or five pin would normally be for three phase.
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These "Commando" plugs/sockets don't have a fuse so should at least match the breaker and cable of the supplying circuit. Don't put a 16A socket on a circuit with 32A RCBO.
Predictive text I suspect. Its a pain!Good spot, no idea where "understand" came from in my post.
Re regulations, a board that was compliant to an earlier version of the regs is still compliant. Requirements for new installations don't get applied to existing installations.
Thanks.Sorry Scotl but this is not true mate.
If you take a look at the Electrical Safety First best practice guide 4: https://www.electricalsafetyfirst.org.uk/media/tx5i50ao/best-practice-guide-4-issue-7.pdf
Check out the last paragraph of the introduction, it puts it into words better than I can.
In response to the OP; do be aware that there are other essential factors to consider before replacing an MCB for one of a different type.