Electrical woes

[Bluekingfisher]

Gents, I have just moved my new machines into my newly built workshop (today) and I have two problems which may or may not be connected????

First, I spent the day assembling my table saw, (I have a thread on this about a year ago) anyway, having put it all together I fired it up, fine, no probs. Cut a couple of bits of timber then turned it off. After about 20 mins I went to start it again, it started them immediately died. I checked the fused and found it to have blown. Replaced the fuse and fired it up, again no probs then same again, fuse blown??

Second, I tried a couple of other machines and they seemed to work fine, then I tried my planer (which has a new NVR switch). It starts OK but the switch doesn't hold and as soon as you release the "on" button, it cuts out. I checked the connections and they seem good and tight. When I moved the machies in I had to roll them across some cobbles which was a bit of a rumbling journey across the patio, was wondering if this could have shaken something loose?

The othwer factor to the equation is the workshop itself. It's new with a new ring main. I had an electrician fit an RCD rated at 16A from my main board in the house. From here I have run about 20m of 6MM cable to a fuse board in the workshop. I have 18 sockets in the ring on 2.5mm cable. The ring is a contious loop back to the workshop fuse board. The fault? doesn't trip the MCB in the workshop or the RCD in the house.

Any ideaas what might be happening folks, what is the first thing to check? bearing in mind everything else seems to work OK. the table saw has a 3HP motor and the planer 1.5HP motor.

Any thoughts would be greatly appreciated. Very frustrating having spent the spring and Summer buuilding the place then move in only to find the tools won't work

Thanks in advance folks

 

[paulm]

There are others more experienced in these things than me on the forum, but I would suspect your tablesaw needs a 16 amp circuit given it's start up power requirements and motor size.

Less sure about the planer.

The 16amp RCD from the house supply doesn't sound right also and a 20m run of 6mm cable sounds a bit on the light side also, but don't think they would be causing the current problems, although they may cause other problems if you have any significant amount of power demand in the workshop such as tablesaw, extractor, heater etc running at the same time.

Hopefully someone will be along shortly with some more specific thoughts.

Cheers, Paul

 

[RogerS]

Gents, I have just moved my new machines into my newly built workshop (today) and I have two problems which may or may not be connected????

First, I spent the day assembling my table saw, (I have a thread on this about a year ago) anyway, having put it all together I fired it up, fine, no probs. Cut a couple of bits of timber then turned it off. After about 20 mins I went to start it again, it started them immediately died. I checked the fused and found it to have blown. Replaced the fuse and fired it up, again no probs then same again, fuse blown??

Fuse where? In a 13A plug? You need a dedicated 16amp radial feed from your workshop consumer unit. It's the switch-on surge of the table saw that is blowing the fuse.

Second, I tried a couple of other machines and they seemed to work fine, then I tried my planer (which has a new NVR switch). It starts OK but the switch doesn't hold and as soon as you release the "on" button, it cuts out. I checked the connections and they seem good and tight. When I moved the machies in I had to roll them across some cobbles which was a bit of a rumbling journey across the patio, was wondering if this could have shaken something loose?

If it was an old NVR I'd have said that dust/wood has got stuck in the contacts and so a blast of compressed air is a good way to try and clear it. But it's new and so could be a loose connection. Mind you, a blast of air is worth trying.

The othwer factor to the equation is the workshop itself. It's new with a new ring main. I had an electrician fit an RCD rated at 16A from my main board in the house. From here I have run about 20m of 6MM cable to a fuse board in the workshop. I have 18 sockets in the ring on 2.5mm cable. The ring is a contious loop back to the workshop fuse board. The fault? doesn't trip the MCB in the workshop or the RCD in the house.

Confused. What 'fault'?

 

[9fingers]

Don't use that electrician again!

The mcb in the house needs to be uprated and the CU in the workshop needs a 16 amp type C breaker dedicated circuit to a blue 16a socket for the saw. There is no way you can run 3hp saw on a 13amp plug.

Your ring of 13amp sockets meed a 30 amp type B (conventional) MCB

It looks like your planer NVR has a loose wire but if it is the cheaper type, the coil may be open circuit.

You might be better off getting another electrician to look at your installation.

Bob

 

[Bluekingfisher]

Thanks for yopur swift response gents.

RogerS - Yes, the 13A fuse which keeps blowing is the fuse in the plug (Brand new saw with a standard 13A plug fitted).

On the dedicated feed, is 2.5mm cable enough or should I look aty using some of the 6mm cable I used to supply the workshop, I have plenty left over?

Bob

On the matter of the NVR switch, is there a simple way of testing the switch, although brand new also it is one of the £25 versions from Axminster, unfortunately I bought it about a year ago and worked fine but the tools have been stored for a year so shouldn't have any dust probs but will give that a go.

With regards the Blue 16A socket, is that the round two pin type seen on 110v site tools, apologies for the ignorance gents.

Thanks again.

 

[Benchwayze]

I had a similar problem with the NVR switch on my Coronet Major Machine.
Just a 1hp motor that up 'til then, had always worked without trouble.

As soon as I released the green press switch the thing switched off. It turned out that the pad on the start button itself was not lined up correctly inside the switch housing. I opened the casing and a judicial bit of fiddling solved it.

Not saying this is your problem, but it's worth a check.

Regards
John

 

[9fingers]

A single run of 2.5mm from the consumer unit in your workshop (NOT the house) is adequate for a 16a blue socket.

A 16a blue socket has three pins as do site 110v ones but they are yellow and must NEVER EVER be used for a 240v application.

Do make sure you fit the correct sex of blue plug/socket. One with holes on the wall and one with pins on the flexible lead to the saw.

John - Benchwayze has probably put his finger on your NVR problem.

Please don't take this the wrong way but I really feel that from your previous comments in this thread that you may not be classed as 'a competent person' within the meaning of the 'act' to be doing electrical wiring.
I know you had an electrician in before and I can't understand why he did what he did by connecting up heavy (correct) cable to such a puny MCB.
For your own safety, please give serious consideration to getting first hand qualified help.

Bob

 

[Bluekingfisher]

Thanks gents again,

John,
I'll have a closer look at the back of the switch, they are cheaply made, from China no doubt but as I said, I fitted it, made sure it worked by switching it on and off a couple of times then set it aside for storage. Perhaps me dragging it across the yard has shaken something loose.

Bob,

I am definitely not an electrician but like to take advice from competent sources then apply what I have learned. Obviously I know my limitations and cautious when I encounter a problem, particularly when it comes to electricity.

The other point which I have to elaborate on is that I supplied you with the wrong info initially. On your recommendation of seeking another electrician I checked my initial post. The new unit in the house is rated at 80A with three new ways as my original consumer unit was full. It was installed to service the new 9.5KW shower (40A) with 10MM cable (just under a 3m run from shower to CS) when I installed our new bathroom and two other MCB's rated at 20A each, one of which supplies the workshop and the other is currently spare. I think the 16A I quoted was what I informed the electrician I needed for the workshop, rather than the unit being 16A in total. Apologies.

Also aware the 110V sockets (yellow) are not suitable for my requirements, just a poor analogy of the two round versions of plug.

The ring in the workshop is served by a 30A breaker (shown as 32A on the breakers) with the lights off 6A breakers. I have a couple of 30A breakers spare on the consumer unit so no problems having a dedicated supply for the table saw. Having said this I am confused as to why the manufacturer (JET)supplied the saw with a 13A standard plug?

I have another question to ask of you if you don't mind. Bearing in mind I will now be running a cable for the tablesaw could I have two sockets on it as I intend to upgrade to a 3HP Bandsaw in the near future or would this put me in a position I am in at the minute.

Thanks for your patience and understanding.

David

 

[9fingers]

Hi David,

Things are looking better now you have described the set up.
I too am not a qualified spark and so try not to get drawn in to these discussions but I have this time :lol:

I *think* the 'letter of the law' is one 16a socket per radial cable (1.5mm or greater) from your CU but I cannot see any real safety issue with fitting 2 x16a on the same radial cable provided there is a 16a (ideally typeC) fitted in the workshop CU.
As a single user (i assume?) you are not likely to be running two machines at the same time and if the total load were to 16a for any length of time the MCB would protect the wiring.
So I am not saying you should do this but it is what I would do in your position. :wink:

13a plug on high power machines?? well it happens and possibly if the mains voltage is at its highest limit and the cable is short form the CU they might get away with it. One thing is for certain, fitting a 16a plug on would put some customers off from buying. Sharp practise? maybe so.

My 3hp saw motor is marked at 19 amps and certainly pops 13amp fuses
my 1.5hp planer will also pop 13amp fuses as it is both on a long lead and has to spin up a heavy cutter block.

Hopefully you are on the right track now.

Good Luck

Bob

 

[Bluekingfisher]

Thanks again Bob, sorry for the initial confusion.

I am a single user so no issues with simultaneous use of the machines but as I have the capacity in the CU I will go with a single socket for each machine just to be safe. I just hope I can find a 16A MCB compatible with my workshop consumer unit, but thats another story.

David

 

[les chicken]

Bob

I hate to disagree with you but my sip 01332 3HP table saw runs quite happily of a 13 amp plug. One of the reasons why the fuse will blow on start up is that the drive is too tight. If the machine is belt driven the usual cause is that the belt drive is too tight, requiring more amps at start up. This is not good for the machine as it will cause bearing wear as well as more amps to cut wood. I suggest if the machine is belt driven to check that the belts are not too tight.

Les

 

[9fingers]

Les,

I certainly did not mean to say that a 3hp saw won't ever run on 13 amp plug.

A lot depends on how quickly the motor will get going. This depends on a plethora of things, some of which you can alter - such as belt tension and other things like the motor design which you can't.
If the mains supply is at the upper limit of its range, the power available for a given current is significantly higher leading to a fast start. The real killer I find is a long cable with high voltage drop which really extends the start up time and pops the fuse.

Cheers

Bob

 

[Bluekingfisher]

The saw is belt driven by a single flat belt approx 25-30mm in breadth, if memory serves. I hadn't considered the effects of the belt being too tight may have on the machine. I will check that as a matter of course once I get to set the saw up.

The cable is approx 2.5m in lenght, assuming you mean the plug cable for the saw or do you mean the cable from the CU to the outlet (which is about 7m.

All said, I am now looking at installing a dedicated 16A supply anyway. With its own supply it should reduce the risks of tripping if I have other machines running at the same time such as my dust extraction, air filter etc. The only problem I have going the dedicated supply route is trying to source a 16A MCB for my CU. A couple of the electrical outlets I have tried haven't heard of the make (Contactum) which is a shame as I could do without replacing the CU

Would upgrading the cable of the saw help any? it seems a tad light in gauge.

On the matter of the NVR switch, I took the advice given and stripped it down as far as it would let me, it now works, no doubt something must have shaken loose :duno:

 

[9fingers]

David,
Stick with your plan to move to 16amp - it will be better in the long run.

Contactum don't list type c breakers in their online catalogue.

I suggest you take an existing breaker from your CU along to an electrical wholesaler and compare the position of the DIN rail cutout on the back and the position of the busbar entry. These are the main differences between brands and you need to make sure they line up. A further nice to have, is the position of the bezel and operating lever but if these don't line up, then the box opening can normally be filed to fit.

Cable lengths of 10s of metres will have an effect, not the short bits you are talking about.

Bob

 

[Bluekingfisher]

Bob,

Just my luck with availability of MCB's, a trip to my local CEF or TLC will hopefully turn up trumps with a compatable breaker.

Thanks again for all your assistance on this matter, much appreciated.

David

 

[9fingers]

Bob,

Just my luck with availability of MCB's, a trip to my local CEF or TLC will hopefully turn up trumps with a compatable breaker.

Thanks again for all your assistance on this matter, much appreciated.

David

Just looked at the TLC cat (may /June 2010 issue 316) and see that they show contactum type c MCBs
order code CM9016C for the 16 amp version £5.90 ea

hth

Bob

EDIT

http://www.tlc-direct.co.uk/Main_Index/ ... index.html

You might have to order these as they are from their extended range.

 

[Bluekingfisher]

Just had a look at the TLC website and the Contactum MCB's, they look very very similar, albeit a newer version. I have a TLC in Huntingdon so I'll pop in at the weekend with one of my MCBs as a comparison.

I was hoping to do the work this weekend but bought a planer on ebay last night, it's down in South Wales. I convinced the wife that a trip down and a night out was reason enough to buy it.

I'll just have to sell the one I have now, if you know anyone interested in a planer put them in touch.

Regards

David

 

[Stoday]

The electrical installation described is poorly designed, does not meet the BS7671 wiring regulations although it is safe.

The whole workshop is fed from a 20A MCB, yet the workshop power is through a ring circuit with a 32A MCB. This means that a fault on the workshop ring will trip the house MCB and not the local MCB in the workshop. The 32A workshop MCB will never trip! That is what's contrary to the regulations.

The 6mm cable from the house could be protected by a 32A MCB; at 20A it's under rated. So my suggestion is to swap the 20A MCB in the house for a 30A MCB that you have spare (I'm guessing the house unit will also be contactum). You then have a 20A MCB for the dedicated radial to the saw.

There's no need for a plug and socket with a dedicated radial — I'd much rather wire to a 20A isolator and connect the machine to that.

 

[Bluekingfisher]

Stoday,

I take your point and very valid re my current set up and one to be honest I had overlooked.

Unfortunately the main CU in the house is a flush fitting unit with no spare MCB to utilise. As a result a new unit has been T'd off this, primarily to feed a new electric shower we had installed. The new unit, rated at 80A has a 40A MCB (shower) 20A workshop and 20A spare. I don't think the MCBs from the new CU and the workshop CU are compatable so your suggestion is not possible. If the new unit permits, would it therefore be possible to replace the 20A shop MCB with a 30A mcb. Would this then require me to remove the spare 20A MCB to prevent exceeding the 80A rating?

Could I supply the ring in the WS with a lower rated MCB to ensure it would trip rather than the MCB in the house?

Although the WSs is for hobby use only and therefore not so much of an issue with rBritish Standards, H&S etc I would however prefer to have it done correctly.

The other issue with the tablesaw linked straight into the radial supply concerns me. I would prefer to be able to unplug the saw when changing blades and for maintenance etc.

I welcome your thoughts.

David

 

[Stoday]

I don't think the MCBs from the new CU and the workshop CU are compatable so your suggestion is not possible.

That's a shame. I assumed that both the new and workshop CUs were added at the same time and therefore used the same make of MCB.

If the new unit permits, would it therefore be possible to replace the 20A shop MCB with a 30A mcb. Would this then require me to remove the spare 20A MCB to prevent exceeding the 80A rating?

Yes, it would be advantageous to replace the 20A MCB with 32A. The 80A CU switch rating is not based on the sum of the MCBs' ratings. Normally, the sum of the MCB ratings would exceed the main switch because the circuits will not all be fullly loaded at the same time.

Could I supply the ring in the WS with a lower rated MCB to ensure it would trip rather than the MCB in the house?

Yes, with a 20A MCB. If the simultaneous load on your workshop power is greater than 4.6kW (20A) you could split the ring into two, connecting each part to a 20A MCB.

The other issue with the tablesaw linked straight into the radial supply concerns me. I would prefer to be able to unplug the saw when changing blades and for maintenance etc.

Plugs and sockets are generally considered less safe than a permanent connection. The connection is not directly to a radial; the machine is connected to the isolator on the end of the radial. You then have two means of isolation: the isolator itself and the isolator in the workshop CU.

The old advice about pulling the plug was because most switches associated with 13A sockets can't properly isolate the appliance because they don't break the neutral.

As for the choice between 16A and 13A sockets, the 16A has the advantage, for a workshop, that it does not have a fuse. Therefore it can carry a motor starting transient without blowing a plug's fuse. (the protection is from a 16A MCB in the CU, which can be a type C curve if starting transients prove to be a problem). The disadvantage is that it cannot be connected to a ring circuit or a 20A radial.