Fuse blowing BS400

[NetBlindPaul]

Digit,
We aint gone into fault finding the machine yet!
However, yes you are correct IF the overload lasts over 5 seconds at 32A then at some point, the fuse will rupture.
However, the exact point of rupture is not easily defined, it is certainly not defined in BS7671 as far as I can see as I have my copy along side me at the moment

I have a much simpler device than a DSO to do this, however, it is a dedicated piece of test equipment.
However, as this is the sort of fault upon which I pay my mortgage then it is only to be expected IMHO.
Any "spark" attempting to diagnose such a fault must have the competence and equipment to undertake adequate testing!

The motor may have an electro mechanical brake, which could be malfunctioning?
This would also restrict the ability to rotate the motor with the power off, even of there were no fault present.

 

[Digit]

This would also restrict the ability to rotate the motor with the power off, even of there were no fault present.

Yep! But bandsaws are notorious for dust in bearings, first things first. After all, there's not much point in dragging an electrical engineer in if the bearings are tight.

Roy.

 

[NetBlindPaul]

Digit,
Correct, though my previous point about electrical engineers still stands, I doubt that many would come out to look at a diy bandsaw!
By the by, dust in bearings is a very valid point, but if the machine has an electro magnetic brake it may not be possible to rotate the motor with the power off anyway as the brake will clamp the rotor to a standstill. Unless this could be disabled.
It may not be safe however to attempt to work on the motor with any electrical power to the machine

 

[9fingers]

It's been a while since this thread started but I'm pretty sure this was a new machine - so there should not be faults.

Bob

 

[Digit]

Once again I would agree, but I covered that with a question to GT as to whether it is belt driven or direct drive.
When he comes back with some answers we may be able to move him along.

Roy.

 

[Digit]

Agreed Bob, in fact I rather doubt that it has a fault. If GT has overtightened the band, for example, the start up load will rise, he also stated that he used it many times then states it blew 4 fuses.
From that I conclude that it ran sometimes, and as I pointed out to Paul, fuses may well stand a high overload once or twice, repeating that overload will eventually rupture the fuse.
If the machine is new then it's reasonable to ask what the line voltage is when the machine starts up, if that's OK then I suggest that a 13 amp plug is not suitable.
My table saw was supplied with a 13 amp plug, and like GT's BS, it blew fuses at various times.

Roy.

 

[NetBlindPaul]

Digit,
I fully understand the thermal stress on fuses, it is something I have to explain regularly to my customers when fuses fail for no obvious reason.

Now you took it that the fuses blew after a few starts, I took it that the fuses blew on every start?...

This is one of the problems trying to fault find machines over the internet!!!

IIRC the BS400 is belt driven, and as has been suggested, there can be several reasons for increased starting current, blade & belt tension being the most obvious.

The volt drop issue is what I think I intimated in an earlier post, just because the final circuit from the local DB is on a 16A breaker to its own 13A socket, we do not know the length of this final run, whether this is fed from the origin of the installation at the main fuse box nearest the DNO cut out/meter.
If it is on a sub main, is the sub main adequate for the overall load?
Is there excessive volt drop in the sub main, if there is one?
Is there excessive volt drop in the final circuit.
For a motor load there may well be.
Is there adequate capacity in the incoming DNO supply cable?
This could be looped form next door believe it or not, we don't know.
This may be a mechanical issue all along, perhaps there is a tight bearing in the motor/bottom pulley/top pulley.

Now 1.5mm sq flat twin & cpc will carry 20A when clipped direct to a wooden or masonry wall. Reference BS7671:2008 Table 4D5.
However, with a starting current of 32A and say a nominal starting voltage at the mcb of 230V a.c. (the official UK voltage), say a 10m run of cable, you would have around 7.4 volts dropped, (BS7671:2008 table 4D5) thus your machine voltage at the socket outlet would be 222.6V.
The machine cable would be around 2m?
This will almost certainly be 1.25mm sq flex, this carries 13A, (BS7671:2008, table 4F3A), value engineering suggests that if the machine maker considers a 13A supply cable to be adequate then they will not fit a larger one as this adds cost for no benefit, thus reduces the competitiveness of their offering. This flex alone would add another 2.4 volts drop (BS7671:2008, table 4F3B) , thus now at the machine contactor you are looking at 220.2V, then there is the volt drop in the machine wiring out to the motor.
This becomes significant, you may see as low as 210V a.c. at the motor terminals for the instant of start up.
This does not allow for DNO volt drop in their install or any wiring between the DNO cut out & the final circuit MCB.

This IMHO is why 5DW can struggle with domestic installs when “industrial type” loads are added. This may not be the case.

However, there is a reason for this issue, and with the information we have and the access we have to the actual install & machine, which in my case is none, all I can do is theorise and make suggestions that need to be considered by those who do have access to the machine & install, the same as the rest of us.

The fact is, if, it is an electrical issue, then the fault has not yet been found, therefore I would say that not enough testing has been done!

 

[Digit]

However, there is a reason for this issue, and with the information we have and the access we have to the actual install & machine, which in my case is none, all I can do is theorise and make suggestions that need to be considered by those who do have access to the machine & install, the same as the rest of us.

The fact is, if, it is an electrical issue, then the fault has not yet been found, therefore I would say that not enough testing has been done!

Yep! I remember telling students that, "out there is someone who has the info you need. Getting it out of them is like getting teeth out of a Duck!"
The number of times I've been told, "it stopped!"
No doubt you've been there as well! :lol:

Roy.

 

[Gordon T]

Hello all,
I will do my best to answer the last two pages of questions.
The machine is a brand new Record BS400. it came with a 13amp plug and has blown fuses regularly every time I have used it.
My installation is 30amp MCB in the house fuse box, 6mm sheathed cable to the workshop which now has a brand new fuse box with a 16amp MCB radial 4mm cable to a 13amp plug socket.
I was also suprised that a commando unit like the one pictured above was not fitted.
The ring circuit to all the other sockets has a 20amp MCB.
The machine will cut several times then blow a fuse, or start the day blowing a fuse.
The motor will start every time when the belt is removed ie no load on the motor.
the bearings are free running, the wheels turn by hand easily enough, the brake does not seem to bind.
The electrician used a megga meter to check all my wiring, sockets, earthing values and a thing with a red claw like end which measured the voltage drop and ampage on startup etc.
The voltage started at 240 and dropped to 239on startup
32amp startup drain with 5amp running drain.
The figures and the part p certificate have not yet arrived in the post so I can not quote them.
Record tell me they have not had this problem with any of the other machines they have sold.
They say it must be my wiring, but just how much more can I do,
I just get on and use it and keep putting fuses in it.
If as suggested I fir a commando unit to solve the fuse blowing, this would if I am right eliminate the 13 amp fuse, then this would solve my problem.............then why was it not supplied with one,
The fact is this is my seventh Record machine and the first one to cause me any problems like this, how much more money and time and effort is this going to cause, when I have the manufacturer telling me its my wiring at fault and my electrician telling me it is not?
Almost forgot Bob,drivebelt tension is fairly slack, and blade is not overdone in my humble opinion.
As a non electrician, I find all this very frustrating, but if fitting aq commando unit will do it I will have a go at fitting one

GT

 

[Digit]

The machine will cut several times then blow a fuse,

Do you mean it will 'cut out' or saw several times before blowing the fuse?
Is the motor getting hot?

Roy.

 

[Duncan A]

Gordon

Induction motors typically take 6 to 8 times full load current for a brief period on startup. This is quite enough to stress a fuse so that it blows after a couple of starts, or even to blow it on the first attempt to start. Axminster suggest fitting a 20A supply to the (1.9kW input) Jet 16" Bandsaw and a 16A supply to their own (1.5kW) AP4300 16" bandsaw. This is in recognition of the fact that they are too big to start up on a 13A plug. Even my 18" Jet bandsaw (2.6kW input) came with a 13A plug which is no use at all, but I read somewhere that there may be a regulation stating that a 13A moulded plug must be supplied.

I suggest you purchase a blue commando plug and socket and your problems will be over, for a very modest outlay.

Hope that helps

Duncan

 

[Digit]

Exactly! That is why I said to 9F that I suspect that there is nothing wrong with the machine. Just run it on a sutable plug/socket/MCB and your problems will probably be all over.

Roy.

 

[9fingers]

Exactly! That is why I said to 9F that I suspect that there is nothing wrong with the machine. Just run it on a sutable plug/socket/MCB and your problems will probably be all over.

Roy.

Which in turn is what I suggested to the OP on 7th Feb in reply to the original question.

We are all violently agreeing :lol:

Bob

 

[Digit]

My memory doesn't go back that far Bob! :lol:
I'm at a loss as to why the sparks put in a dedicated radial main and a 13 amp socket though.

Roy.

 

[9fingers]

He can't have been a real spark Roy!

 

[Digit]

Certainly not a bright one! (sorry!)

Roy.

 

[Stoday]

Hello all, today I plugged my extension lead into the kitchen ran it out to the workshop plugged in the new bandsaw and it worked every time I turned it on!!!!!!!!!

No need to run the extension from the kitchen; you could have plugged it into a workshop socket with the same result. Indeed, that would be the cheap fix — "lose" an extension lead in your workshop. But I guess you want to do the job properly.

If the sockets wiring in your workshop is a radial on a 20A MCB, then you can add as many 16A sockets as you like (provided you don't exceed 20A by the machines you want running at the same time). You are allowed to do this yourself.

Unfortunately, most garage/DIY workshop sockets are connected to a 30A ring. The regulations don't allow you to add 16A sockets to a ring. You would have to connect it through a 13A FCU and you'd get the 13A fuse problem back. Your electricain would have to add a new 20A radial circuit for your 16A socket. You are not allowed to do this yourself unless you jump through some Building Control hoops that will cost you more than employing an electrician.

 

[ondablade]

I'm guessing the issue regarding fitting a 16A plug and socket is the implications for warranty - and for fairly good reason in that if the saw throws up other problems you could be left with it. You could possibly refit the 13A if needed as long as it's not sealed on.

It seems to me that one very basic option is to take Record at their word to the effect that it should run on a 13A socket - not some special socket, but any reasonable socket. It isn't, and they won't it seems help - so put it in the car/trailer, drive it down to wherever it was bought and metaphorically speaking slap it on the counter and demand a replacement or your money back.

You could demand they test it on the spot with a 13A socket, but you would in that case risk it not performing to order.

Some other possibilities to consider. (1) Bum/slightly low blowing fuses - buy a few alternatives by other makers to try out. (2) I don't know quite what the mechanism is, and you may have covered off this possibility - but I know from experience that it's possible to get a rogue 13A socket that for some reason (like maybe a bent/misaligned contact - which might suggest the possibility that a poor contact elsewhere might have the same effect) causes fuses to blow when starting a motor when others do not.

It seems likely that many of these makers of small machines sail close to the wind to be able to sell a machine that runs on a 13A socket - so maybe (3) you have got one where various tolerances are stacking up to leave you on the high end of the current draw - which requires replacement unless they are prepared to have you run a 16A socket.

 

[Digit]

But one mystery remains Ian. Why does it run on an extension lead from the house?
The 'logical' deduction is a line fault between the 13 amp socket and the incomer connection point.

Roy.

 

[CHJ]

Extension lead is introducing resistance I would think, reducing surge current due to momentary voltage drop.

The better the wiring, bigger gage shorter length etc. the greater the surge current is likely to be, the new system is probable making the chances of blowing the fuse even greater.