Fuse blowing BS400

[Gordon T]

Hello again, I must learn to be more clear, when I said the machine cuts several times I meant cuts pieces of wood, then blows a fuse.
Out of interest Record rang me yesterday to ask if my machine was running ok ans sounded suprised when I related my problems and attempts to solve them.
The substation is about 150 yards down the road from me,
and yes I have tried using an extension cable in the workshop, but that time it blew the fuse in the extension, and yes I have tried different extension cables with same result.
Why I wonder would using a commando unit as recommended previously, not work???? surely it would remove the weak link ie the 13amp fuse or I looking at this too simply!

 

[9fingers]

Hello again, I must learn to be more clear, when I said the machine cuts several times I meant cuts pieces of wood, then blows a fuse.

Why I wonder would using a commando unit as recommended previously, not work???? surely it would remove the weak link ie the 13amp fuse or I looking at this too simply!

Yes Precision is vital! do you mean that the saw will start, perform cuts and then on the next start, blow a fuse? or does it blow a fuse DURING cutting?

Provided that it is the former then fitting a 16amp plug and socket will solve the problem (99.9% - I will bet a pint on it!!)

Bob

 

[Digit]

I'm with Bob!

Roy.

 

[NetBlindPaul]

^ As Bob & Roy, as long as the plug is competently fitted I doubt it would compromise your warranty, though I am not in a position to guarantee this.

We could do with understanding the failures of the fuse, i.e. every start, every few starts, when cutting etc.

Paul

 

[9fingers]

I'm with Bob!

Roy.

Mwah! Big hug? OK maybe not then :shock:

Bob

 

[Digit]

Promises! Nothing but empty promises!

Roy.

 

[Eric The Viking]

Right you two! Get a shed somewhere...

Seriously, I've been keeping out of this discussion (better men tham me, etc.), but I do wonder if 'fixing' it with a 16A fuse-less plug/socket might actually be exposing a bigger problem:

If the right measurements were made, we'd know, but it seems the startup current is, well, pretty big for a machine of that sort. It's nominally 1.5kW after all.

Could it be that the starter winding either has a few shorted turns or is wound to the wrong spec? One does wonder a bit.

You'd hope Record would be taking more of an interest really, as the other obvious thing to do is test by substitution. Assuming one was available, I'd start by swapping the entire bandsaw, and if that cured the problem, go back and swap the motor in the bad one. If that doesn't work it's too much friction in the mechanical parts, if not, er, it's the motor.

If neither bandsaw works consistently in that situation, it's the wiring (or both being faulty!).

Perhaps I'm missing something...


E.

 

[Digit]

Seriously, I've been keeping out of this discussion (better men tham me, etc.), but I do wonder if 'fixing' it with a 16A fuse-less plug/socket might actually be exposing a bigger problem:

Yes! GT is trying to help but we still don't know, for example, if the fuse blows mid way through a cut, or at start up after having been turned off after a number of cuts.
My TS drove me nuts at one time, it would turn off then straight back on again. The fuse didn't even wave good bye!

Roy.

 

[Gordon T]

In an effort to help, the fuse fuses/blows always on start up and never during a cut.
The motor starts the blade begins to spin then within seconds and before full running speed the fuse goes ( and not for a walk). But not every time, which is why I have one of the channels in the bed full of fuses, and a screwdriver at the ready .

The switch has been replaced by Record, this was their first dfiagnosis.

Then a new motor arrived and I fitted that but no improvement, so I swapped it back for the original one.

Then the new fuse box fitted etc etc,

and thanks guys subject to what Record come up with next, I will fit a commando switch if nothing else works.

To answer an earlier suggestion, I suggested them taking the bandsaw back for them to test, but having already paid £95 for delivery to my place, and being told I would be paying for redelivery the same amount again once they found no fault with the machine I decided against it, my pockets are almost empty now.

Hope I have coverred all points raised, sorry if I have not answered all , will try to do so.

GT

 

[Digit]

GT, the machine runs on the domestic circuit.
Therefore we know two things.
1-there is nothing wrong with the machine.
2-the problem lies with your workshop supply.
After those conclusions we can only surmise, one of the possibilities is the 13 amp socket itself, I've known them duff new from the box.
If you have another suitable circuit in the shop, connect to that and let us know. If you don't have another circuit but have another 13 amp socket available, please swap them and let us know.
Each step will help narrow the problem.

Roy.

 

[Stoday]

To fix a fault you first have to find it. So you work out what you think it is and test a cheap fix. If that confirms the fault is what you thought, you can make a permanent fix; otherwise start over with another theory.

Circuit protective gear such as fuses and MCBs protect the downstream circuit, not the upstream. In this case, the 13A fuse protects the bandsaw and its connecting lead. The 16A MCB, the radial circuit to the 13A socket; the 32A MCB in the house, the cable to the workshop and the consumer unit in it. So it's difficult to think of anything upstream of the 13A fuse that could cause it to blow or the machine to overload, unless the machine itself were faulty. The rather remote possibility of the proximity of the substation is ruled out because it's quite a long way away.

The commando fix will cost. It provides a better connection than the 13A plug & socket. You can test the effect of a better connection cheaply by swapping the 13A socket for a 20A switch (£2.55 from Screwfix) and connecting the machine directly into it, since it's on a dedicated radial protected with a 16A MCB. Of course if the perceived fault is that the machine blows 13A fuses, eliminating the fuse cures the fault. But it's the real fault that is causing the fuses to blow; eliminating the fuse won't cure the real fault that still there.

I'm not so sure there's nothing wrong with the machine. Record has no other customer who can't run their machine using a 13A plug & socket. My table saw uses a more powerful (2kW) motor on a 13A plug & socket and I haven't blown the fuse (or tripped its MCB) in six years. That suggests that if the machine won't run without blowing a 13A fuse, it is faulty.

Although ETV's suggestion that the starter windings might be faulty was plausible, it's ruled out because GT swapped the motor as well as the starter switch. That leaves the possibility of a mechanical problem that's extending the time it takes to get up to speed, thus causing the starting transient to take too long. Perhaps there's a way of checking this out.

 

[Digit]

I can't see how the machine can be suspect if it runs on the domestic circuit S.
Upstream faults would be difficult to suggest, I agree, but what else is there?
With the machine running on the domestic circuit a machine fault would have to be intermittent, hence, damn difficult to find.

Roy.

 

[Eric The Viking]

I'm a fan of the too-low source impedance theory myself .

- Knowing that the motor has been replaced eliminates the original motor.
- GT has told us the machine turns freely with no obvious friction or binding.
- Introducing impedance (extension lead from the house) keeps the fuses intact. It's a reasonable working assumption that the house supply has a higher impedance than the workshop (as that's just had new heavy cable, etc).
- the local xfmr (sub-station) is relatively close. If this is a semi-rural or rural area GT's property may have a nice fat bit of copper in the road, with few other taps off it before his.
- It hasn't yet been tried on a fuseless 16A circuit. Bob M. reckons that a 16A plug/socket will fix it. I think he's right.

Goodness knows how you might measure the source impedance of the mains (I think I was probably told about 30-odd years ago but have long since forgotten), but if someone did it, my guess too is that it would be atypically low. As long as the motor is happy with the startup surge as it could be in those circumstances, and it probably is, then there's no real problem beyond fitting a blue plug+socket.

Weird stuff, electrickery.

E.

 

[Digit]

As long as the motor is happy with the startup surge as it could be in those circumstances, and it probably is, then there's no real problem beyond fitting a blue plug+socket.

If that turns out not to be so then by heck it will get to be interesting, ie, weird!

Roy.

 

[Tierney]

Hi,

I thought that rather than start a new thread, I would continue an old one. I have the same problem with my table saw - I think it might be worse due to the cold weather!

Anyway, I think it worked fine in my old house. My new house was completely re-wired, so along the lines of some previous suggestions it may be that unusually low impedence is the problem.

Anyway, the facts are:

Machine
Scheppach TS2500 table saw (the old aluminium top, bought second hand so no option to return it)
I think running wattage is 2kw, startup 2.7kw
The label on the saw states 11.5A; but, the label on the one-off switch has 'IE = 13.5A'

Wiring
My new garage has a separate new MCB in the garage, running off a new MCB in the house, I think the house or the main MCB has new tails (whatever that means).
The cable to the MCB in the garage is either 2.5mm or 4.0mm; just usual domestic stuff
The garage has a ring; I think 2.5mm on a 32A breaker
The saw is connected to an extension lead; both have 13A fuses (only the fuse on the table saw lead blows)

Fault

I think more often than not it now blows a fuse on startup. When it starts it runs fine and has never blown a fuse (even though I am ripping 2" thick stuff on a blade that could do with a clean / sharpen.
I had been spinning the blade and then pressing the start button; which, I think helped; but, not always and it's not exactly safe
As said previously the fuse only blows in the plug on the table saw lead (I think I've gone through 8 now)

Solution
A number of people have suggested using a 16amp plug/socket connected to a 16amp breaker; which, seems like a solution (even if it doesn't mean that I understand what the root cause); however, does it need to be on it's own spur (i.e. not a ring), and does it have to be a 16amp breaker (I have a spare 32 in the MCB, that is the only reason I ask).

I was sort of hoping that I could install a ring of 16amp sockets as I have a large bandsaw and planer, both three phase and about 40 years old - one has a dedicated converter, and the other has god only knows what connected to the motor to do the same. From what I have read on this and other threads, it seems to be that a ring may not comply with regulations if you are using 16amp plugs. Interestingly both never blow the 13amp fuse; but, they do cut-out when starting, so I need to press the start button, then off button and then repeat numerous times allowing them to build up momentum!

Anyway as I said, quite happy to try the 16amp socket; so I guess my question is as much about how to connect that to the MCB, unless I have missed something major, or someone has any other easy ideas.

Regards,

DT

 

[condeesteso]

I have a 500 and first time I ran it, it tripped the 16A supply. Whilst they rate at say 2hp (about 1500 watts i think) they draw a lot more starting ( a short hefty peak). Once running they stabilise, but you may just need to give it more headroom on startup.

 

[9fingers]

16a sockets are fitted to radial circuits, each one protected by an MCB rated at 16a or quite often 20a.
For motor applications, these are better if type C providing the earthing is low enough impedance.
Each radial can be wired in 1.5mm2 cable although unless you have a source, you might just as well use 2.5mm2
You should not install a ring of 16amp sockets

Bob

 

[Digit]

Frankly it sounds like a mess!
It would help if you could tell us for certain whether the incomer is 2.5 or 4 mill, and the length.
The most logical reason reason for your problem is the actual start up current, (as opposed to what it is supposed to be,) this is supported by the cold affecting it.
'Tails' are the leads from the meter to the consumer unit.

Roy.

 

[Tierney]

Thanks for the replies. Ok, had another look and can give some more details:

1) I have a new consumer unit in the house, this has a 32amp MCB (on an unprotected part of the consumer unit, i.e. not through an RCD).
2) The consumer unit in the house is connected to a consumer unit in the garage with what looks like 6mm twin and earth cable (the live and neutral each have about six copper strands of about 1mm diameter). The length of this cable is somewhere between 20 and 30 feet.
3) The consumer unit in the garage has a ring circuit of 2.5mm on a 32amp MCB.
4) I have the saw connected to a short extension lead (only about 6 feet long with four sockets on it).

Hope this makes sense.

Roy, hopefully this sounds less of a mess (well maybe except the extension lead bit), otherwise I'm going to start feeling a bit ripped off. I told the spark and he saw what machines I had.

DT

 

[Digit]

Without carrying out some checks on conducter dia I am not certain but that does not sound like 6mm to me.
As Bob says a 32A ring and 16A sockets is a no no. Physically it could be done, but it would negate the whole idea of correctly guaged protection for the machine.
A dedicated radial main is the answer, the extension leads and lack of RCD is worrying!
You must understand that the MCB protects the machine, it does nothing for you!
If you cannot get an RCD plus a further 16/20A MCB in the existing CU a replacement is on the cards.

Roy.