Tripping Breaker welding

[Darren]

Can someone please remind me what speck breaker I need for a welder?

My MIG is 210A and trips the breaker on the highest setting 

What safety would I loose if by changing the breaker, ie do I need a separate spur or will it be OK on the main garage ring.

Currently have MCB and RCD on the box.

[John Rudd]

Errr 210A.....

That cant be the input current rating surely?


Is there a spec panel on it with the input requirements? 240vAC xx Amps

I'd have thought a 13A outlet would suffice.......

[Darren]

The 210A will be right at the output voltage but not the input. I have no idea what the input is 

My main breaker on the box is a 63A RCD and the ring is on a 32A MCB. I would have thought it would be enough but I'm sure I've read that a slower reacting earth leakage detecting MCB is required .... ?

This I assume allows the transformer input surge to be ignored for a fraction of a second ... or sumut like that ? I only have the problem on the highest setting that flips the trip about 80% of the trigger pulls. So whilst it's almost there it's useless in reality.
I could have done with it last week as I was welding some thicker stuff. Instead i just had to go slower and allow the heat to build up. Worked out OK but was a bit of a pain.

[John Rudd]

My main breaker on the box is a 63A RCD and the ring is on a 32A MCB. I would have thought it would be enough but I'm sure I've read that a slower reacting earth leakage detecting MCB is required .... ?

Just to clarify....the 63 amp rcd is tripping? would indicate a leak to earth...

32amps at 240v is getting on for 8kw plus....Thats a lot of power if the 32 is tripping...

You have a fault with your welder...or else the breaker(s) is tired

[Darren]

The RCD is fine, it's the MCB that's tripping.

There is no fault, it's just that the MCB thinks there is when the welders transformer initially sucks juice from the wall  ........ found it  I have a type B MCB and I need a type C 

http://www.tlc-direct.co.uk/Technical/Distribution/Mcb.htm

[John Stevenson]

The RCD is fine, it's the MCB that's tripping.

There is no fault, it's just that the MCB thinks there is when the welders transformer initially sucks juice from the wall  ........ found it  I have a type B MCB and I need a type C 

http://www.tlc-direct.co.uk/Technical/Distribution/Mcb.htm

Get rid of the MCB and get a JCB.

John S.

[Fred Bloggs]

Darren

My day time job is as building services electrical engineer, if you can tell me what the electrical specs for the welder are, the type of cable which is feeding the welder, its distance from the consumer unit and its CSA (cross sectional area) and I'll calculate what you should have.
I also need to know whether your property is feed from overhead lines and therefore has a TT earthing system , or is your property feed via underground cable in which case the earthing system will be either TNCS or TNS, you need to know this as the earth fault currents and short circuit currents are/can be a lot lower with TT systems especially in rural areas.
Also what type of consumer unit have you got, as you will probably have 32A type b miniture circuit breakers on the ring, the type "b, c or d" refers to the speed at which the breaker will operate at a give current, type b CB's trip at a lot lower current (are normally used for domestic installations) than type c or d CB's, type d are normally used for motor start applications which can have a starting current upto 10 times their rated current.
I do not suggest that you just change your garage ring main circuit breaker for a type c or d as the breaker will not probably clear a genuine fault in the time allowed under BS7671 , "the wiring regs", hence my questions above, it would probably be easier and safer to run a suitably radial feed from the consumer unit to a dedicated socket in the garage (32Amp commando socket with isolator)

Hope I can be of service

Fred

[Fred Bloggs]

Darren

I'm that slow at typing 4 more posts have appeared before I put my reply up, take heed with my previous post dont just fit a 32A type c without a bit of maths!!!!!!!!!!!!

Fred

[John Hill]

Get rid of the MCB and get a JCB.

John S.

Carry it home in your HRG.

[Darren]

Hi Fred,

Thanks for the offer of help, I'm afraid it's been at least 20yrs since I last worked as an electrician and TBH I've shown little interest in it since then. So you could say I'm past my sell by date.

The garage was built last year. All new materials were used esp for the electrical side of things.

My earth is tied to neutral back at the power station. (overhead feed here)

I rightly or wrongly, take your pick, fed the garage from one of the house consumer units (we have three ...erm make that five, but three main ones anyway) That is old but it does at least have trip fuses

From there I took two runs of 4mm 3 core SWA cables 45m long (two of to minimise volt drop as I suspected some larger 3ph motors would be coming my way)

These SWA's feed a new consumer unit with a 63A RCD and a 32A MCB for the ring main (2.5mm T&E 10 sockets, might be 12 I forget offhand)
Lets say the ring is 30m from end to end, it'll be close enough.

I'd go and have a look at the welders ratings, but I doubt it's going to give surge current details.

I'll see if I can find it on the web ..... anything else you need to know?

[Darren]

BTW, I do still get a bit of volt drop at times, it's not constant but the lathe lets me know when. That's in 2HP mode and cold, it's fine when it's warmed up a bit .... usually.

[Fred Bloggs]

Darren

I'll work some numbers with the info you've posted and get back asap work / SWMBO permitting

Fred

[Darren]

Today I plugged one of those electricity monitors into the socket outlet for the welder. I don't know how accurate these things are but it will give some idea of what is going on.

This measures what is happening on the 240V side of things.

The readings were on full welding power.

238V

3.4KW

19A

Though this is within the scope of a 32A MCB I'm guessing it still is not telling us what the surge current is as the trip does it's job a bit quick for the plug in tester to take a reading. But as the trip behaved itself mostly today those readings are under continuous welding at full power.

If I connect the welder to the house socket with only an RCD breaker on a long 2.5mm lead about 35m all works fine. i.e. no tripping.

I really do think it's just the wrong spec MCB for an induction device such as the welder. This problem is quite common.

[Fred Bloggs]

Darren

Apologises for taking a while to get back to you, Family and work and a bad back have priority. Please see the calculations below, Note that due to me not knowing the site I have made some broad assumptions with regard to the electrical characteristics at your property!!

As you have stated that you are feed from an overhead line system (TT system for the electrically minded among you)therefore must assume that the Prospective Fault current at you meter tails is going to be around 600-700Amps – best case and the Earth loop impedance will be in the region of 21 ohms
I do not know what protective devices are fitted upstream of the SWA cable (Steel wire armoured) feeding the garage (Man kennel) so I will have to ignore them for the purpose of the following calculations – finger in the wind guesses??? – ( lots of shouts of sack him at this point from all the PhD’s in electrical engineering on this site)

Calculations

1/ - (Quick check total volts drop is less than 11.5volts (5% of supply))

Assume that 20amps load on system.

1/a/ Ring main  is 18mV/Amp/Meter for 2.5mm² T&E (Twin and Earth Cable)

Therefore Vdrop in ring = (18mV x 20A x 30M)/4
                      = 2.7Volts

1/b/ SWA Cable  is 12mV/Amp/Meter for 4mm² SWA

Therefore Vdrop in SWA = (12mV x 20A x 30M)/2
                       = 5.4Volts

Therefore total volts drop at around 20A load is 8.1 Volts so even if load was actually at 25A due to lights etc in garage volts drop would be 9.75Volts and at 30A load it would be 10.8Volts . which is still (just) under the 11.5V limit.


2/ - Calculation of fault currents and MCB operating times

2/a/ Assume Impedance of the supply is 0.4ohms.

Impedance of the 4mm² SWA cable is 4.61ohms/1000M

Therefore   Impedance for 2 runs of 4mm² SWA in parallel,

Length = 45M       Zswa= 0.207ohms

Impedance of the 2.5mm² T&E cable is 19.51ohms/1000M

Therefore   Impedance for 2.5mm² T&E cable in a ring main,

Length = 30M      Zring = (19.51mohms/M x 30M)/4
                          =0.146ohms

Therefore total Impedance    Zt     = 0.4 + 0.207 + 0.146
                                 = 0.753ohms

But you must apply temperature correction factor of 1.2

Therefore       Zt      = 0.753 x 1.2
                        = 0.9036ohms

2/b/The Fault current at the furthest point of the ring main should be

         Ifault = 238V (measured)/0.9036ohms
             = 265A

From the Wiring Regs (BS7671) the current required to cause a BSEN 60898 Type B 32A MCB to operate in less than 0.4Secs (Requirement of Reg 411.3.2 – portable equipment) is 160A Therefore as the calculated (Caveats noted) fault current is greater than this by 10% (my safety factor), the system as it is complies with BS 7671.

BUT if you replace the existing Type B 32A MCB with a Type C 32A MCB you will not comply with the wiring regs as the Type C 32A MCB requires a fault current of greater than 320A to operate in less than 0.4Secs.!

SOLUTION

Therefore I suggest and it is only a suggestion that you wire a short piece (3meters) of minimum size 6mm² T&E to a 32A commando socket with a suitable isolator and fit a Type C 25A MCB in a separate way in the garage Consumer unit!

This would give a temperature corrected impedance of 0.756ohms

Therefore fault current would be - If  = 238V (measured)/0.756ohms
                 = 314A

This fault current is greater than the current required to operate the Type C 25A MCB, which is 250A ,again this would then comply with BS 7671.

Caveat

Please be aware that the above calculations are based on the limited information I have been given, a site survey might conclude that the exist installed system does not even meet current regulations!!!! That is not a critisim of your wiring skills Darren, just that you have quite long cable runs on a overhead TT system in a rural setting , to quote you “I do still get a bit of volt drop at times, it's not constant but the lathe lets me know when. That's in 2HP mode and cold, it's fine when it's warmed up a bit .... usually.”

For example when the lathe is starting as above there is probably 100A inrush for a few cycles of the mains , given a peak volts drop of approx 30V which is going make the lights dip a bit!!

Anyway I hope the above is of some help – If any of the boffins on this forum wish to comment / tear my thoughts and guess work to pieces feel free

PS I spent ages typing this lot above up in a word document, nice spacings etc and its all c"&*ed up when I copied it onto the forum, arrh well I've tried to correct it, I hope you can understand it.

Best Regards

Fred

[Darren]

Hi Fred,

Thanks for getting back on this. I had a quick scan and basically see where you are coming from. (I think  )

What you are trying to avoid is too much volt drop which would at the same time cause the mains cables to get a bit too hot during a fault overload. If I'm thinking rightly if the cables offer too much resistance this can have serious and adverse effect on the trip devices no mentioning the fact that the device will also be slow to trip, if at all.
Not good if you are personally feeding the electrons to ground 

Yes my lights do dip when a machine is started, as do the lights back at the house. But then this used to happen when the lathe was in the house (basement) without the long run of SWA. Even my little Chinese mill used to cause this effect.

Feeding the SWA is a 32A RCD from the house fuse board. via a very short length of 6mm T&E. Terminated in a metal clad box. The SWA has proper glands at both ends.

I'll have another slower read of your post later and try to digest some greater detail.


BTW, my house is fed by 4mm SWA about 80m where it links with next door and then disappears underground. I have no idea how far it goes then ... but it's a long way.
So by what I can see both our houses are fed by one single 4mm SWA and you could consider our house to be eight bedroom and next door is double the size. In fact part of next door is a totally separate dwelling for their parents.
All from one 4mm SWA.

I considered my 2x4mm SWA to be a little overkill, now I'm wondering if my incoming mains is up to regs !!

Much to ponder ......

[framey]

is this welder running on the ring?
what else is on the ring that may be drawing load whilst the welders running?

[Darren]

Hi, Nothing else except maybe just a radio ....

[Fred Bloggs]

Darren

Sorry for not getting back sooner again!

A few more answers / assumptions to your last post!

"now I'm wondering if my incoming mains is up to regs !!" (be aware that the DNO's follow their own set of rules )

I presume that your property once had overhead cables but has since had underground cable fitted, if so the "SWA" you mention will most likely be concentric cable, see following link.
http://www.batt.co.uk/upload/files/straightconcentric_1253109778.pdf

It looks from the outside like SWA but is not , and is only used by DNO's (utilities), it also has a very small outside diameter, 12mm outside diameter equates
 to a phase conductor having a cross sectional area of 25mm² which is sufficient for an 80Amp feed to a property.

Another thing must remember is that all DNO's apply diversity to properties, i.e. they assume that you will not be using anything like 80amps all the time (for example my house base load during the night is 75watts per hour-300mA but during cooking and washing sesssions can be 10kW/hr for  short periods), the DNO's rely on the periods of low power consumption as cooling off periods for the cables. (had a clients telecomms site supply cable catch fire because the DNO engineers had dropped a B$%^&(k and applied diversity to a 500kVA LV supply to site that runs balls out 24/7, the cable melted and took out the busbars in the incoming panel as well , it was right next to the 11kV sub, lots of fault current when she blew

You also state that the lights dip, I'll bet that its more noticable when the local grid is heavily loaded, especially evenings and Sunday afternoons when all the sunday roasts are in the ovens not a lot you can do about the lights dipping other than putting lots of copper in your system to minimise the volts drop.

Best go as she who must be obeyed is grumbling about me being on the computer again

If you want any more info or questions answered feel free to ask

Best Regards

Fred

[Fred Bloggs]

Darren


Have you finished pondering yet


Best Regards


Fred

[Darren]

Hi Fred,

I have decided to follow your suggestion and use a spare way in the garage consumer unit to feed a dedicated outlet for the welder with a class C MCB. Looking at all the options it seems the best way to deal with the issue.
If that fails then I'll just have to accept that I have what I have.

I was going to use the spare way to feed a nearby shed via a 2.5mm SWA, about a 20m run. Just a simple light and maybe a couple of sockets. Nothing heavy to go in there just some smaller single phase machines maybe?

The concentric cable sounds like a bodge? I can't help thinking that it sounds unsuitable for this row of properties? Our property was once a small 20 bed hotel though half of it has since been knocked down, but it's last commercial use about 2.5 ago was a restaurant with a full commercial kitchen. Therefore I assumed our supply should have been more than up to the of what I would ever be asking of it.
Next door is four properties now joined as one private dwelling recently. But they were all businesses too. Then there was another property on the far end, also commercia,l that has since been knocked down.
On the the other side of us is a public house which closed last year.

All these are fed from the same single cable supply. That's seven commercial properties and now only two domestic remain.
To think my supply may not be up to the task of a small welder sounds ridiculous to me?

Comments appreciated as always ....

[gldwight]

Have you consulted the power company as to what the supply side may
consist of?
Sure seems like there shouldn't be any problem like you're having.

George