I let the magic smoke out of my bench grinder.

[Ed.]

I let the magic smoke out of mine yesterday, I was tigging up a fuel tank on my welding bench and seeing as the tank is 1.6mt long and a bit heavy and awkward to manouver, I had to flip it over to do more welds, anyway to cut a long story short, to make it easier to move, I unplugged the work clamp and put it on the TIG trolley which about 4 ft away, and forgot to put it back on.

Started to TIG again and it wasn't welding right, anyway it came good so I kept on going, about a minute later, I started to smell something, looked around in case something had caught on fire, nope, nothing I could see, kept going, smell kept getting stronger. I thought this isn't good,. I had to stop to regrind the TIG electrode so pulled it out and went to the end of the bench where the grinder was and notice that it was smoking from the base, I thought that it was odd as it hadn't been working for about 20 minutes.

After unplugging it, I noticed that the power cable was smoking as well and had been burnt/blistered in several places. Looked up and the shed had a haze in the air. The TIG HF and the amps must had gone though the trolley down across the concrete up the table leg and through the bench grinder on the way to the tank. The grinder runs still but not going to take any chances as the power cable is shot.

I didn't think that it was possible for the current to go across the concrete floor not to mention the rubber wheels but it must have found a path, whilst writing this I realised that it may also have found a different path to the bench so will have to check out the power leads of the TIG and the water cooler leads in case they were affected as well.

So after all this I am after a better bench grinder, found a few on ebay but the freight up to me is a killer but found that the local "Trade Tools" store also had some of the same type (rebadged of cause) $148 for an 8" and $188 for a 10", both 900 watts so will go down and grab one, most likely the 8" one, they can also take a polishing cone. 900 watt is way bettter than the 350 watt on my SuperCheap one, (gutless wonder it was). I am tired of buying underpowered tools.

 

[cumbriasteve]

The electric could not have went by the route you imagine, sounds like something wrong with the grinder/ lead/switch/plug/wall socket etc etc...not sure how your fused systems work in Aus

 

[mike 109444]

Try puting a meter set on ohms between you trolly (with eart clamped on it ) and your steel bench (with grinder pluged in) Recon it went through the metal trolly, onto the case of your welder, through the mains (earth) into your mains circuit and down the earth of the grinder, across the bench to the job, maybe? (not a tigger myself)

 

[Ed.]

I had a think about how it could made the connection whilst lying in bed last night, and I think the only plausible way it could have done so was via the earth on the water cooler. The TIG is 3 phase and on its own seperate circuit and sits on tall rubber stops, however the water cooler has an earth cable screwed to the case and sits on metal screws on the trolley, so I presume that the current went from the trolley via that earth cable through the extension lead connecting to a wall socket, then through the cable leading to the switchboard and then via another earth circuit to the extension socket powering the bench grinder which was sitting on the welding bench, as the cable was also resting on the bench, the HF broke through the insulation of the cable as well as through the feet of the bench grinder as well.

So I will have to call in a sparky to Megger test the wiring in in the conduit to see if it had done any damage anywhere else that is not visible, I am hoping that it is only the grinder and its' lead that is fried.

Everything else seems to work in the shed such as the fridge and other extension sockets on the walls, so I am really hoping that it is the only damage as I don't want to have to replace the wiring to all the sockets in the shed. I think I will also wire up an earth to the welder case and the welding table to the shed walls.

That will teach me not to pay attention.

 

[chunkolini]

OP says "After unplugging it, I noticed that the power cable was smoking as well and had been burnt/blistered in several places. Looked up and the shed had a haze in the air. The TIG HF and the amps must had gone though the trolley down across the concrete up the table leg and through the bench grinder on the way to the tank. The grinder runs still but not going to take any chances as the power cable is shot"

I have a dim memory of reading about this somewhere. HF starts on Tig tracking back up (earth?) leads and frying mains tools. I can remember putting up a post here asking about it and being laughed at, sounds just like what I remember reading about. Cant remember where I read it though.
Chunko'.

 

[Ed.]

Went down to the local Trade Tools store and picked up a 900 watt 10" bench grinder, this one has enough grunt for me and has 32mm thick grinding wheels, there will be a lot of grinding in those wheels, also will be able to fit a polishing cone to it as well.

 

[shenion]

I have done similar. Usually all I get is HF, no real current. But if the return lead is touching the case of the welders, it runs the current through the welder earth and through the earth lead on my bench drill.

My Airco had a 2" long slit on the top of the case. I know what happened, they set the leads on top and the arc stinger on top with the rod still hot. Probably burned that slit in just 2-3 seconds.

I have a steel bench and always have the return lead clamped to it. I make sure it is not where it will be in the way as I know I'll move it and forget to reconnect it

I need to make a checklist of the Airco. There are 7 switches/knobs you need to change when going from DC arc to AC TIG. Seems I always forget one. I have sat there blowing holes in thin metal until it dawned on me the stick "hot start" was still on.

Meter tests won't mean much. you will have to visually check the wires. You could have melted earth and hot wires just barely apart and over time they could short.

I'd replace the grinder power cord and look inside. Check the welder and cooler wires; they are probably higher gauge so are more likey to be fine.

 

[dannyp]

general rule of thumb if your welding bench is grounded to the welder, don't fix anythgin electrical to it.

if the retun is off the eath of the welder acts as an eath lead grounding theough the case of any eathed kit on the bench, if your very lucky it just kills the power lead to the kit, if your lucky it kills the kit an the lead, if your unlucky you cook up the eath wire in the ring main thats connecting the sockets together.

> guess whitch one i did ?

 

[Rick]

Went down to the local Trade Tools store and picked up a 900 watt 10" bench grinder, this one has enough grunt for me and has 32mm thick grinding wheels, there will be a lot of grinding in those wheels, also will be able to fit a polishing cone to it as well.

Wish I could find something like that over here.