Mains protection

[cowasaki]

What are people’s views on the best way to protect yourself.

I have a large isolation transformer, large variac and bulb current limiter.

What order?
Which devices?

I work on guitar amps and currently messing with valve amps. My current protection method involves discharging caps and attaching leads etc before turning the device on. Sometimes checking things with the power on is useful. It would also be helpful to protect the device as well.

What are people’s views? At the most the isolation transformer goes into the bulb limited and I have just bought a job lot of variacs.

[madires]

That's a reasonable setup for messing with valves. If you have a scope also get differential probes as the scope's ground is connected to earth/PE.

[PKTKS]

Too much wide question...

You must split your targets in (at least) 2:
= protect the DEVICE UNDER TEST
= protect you bench hardware

First is kinda what you have - isolation transformer
which should have proper fuse or tripping devices

The variac is essential on faulty devices and
the bulbs are essential too. You just can not afford to
power dead short DUTs adhoc.

The second problem is what sort of installation
your bench use... complex thing to setup.

You need to consider  a list of things regarding your
mains, type of hardware for test and devices under test

My personal setup uses individual isolation transformers
for DUT and for all my bench hardware. And YES I am aware
that some folks advice to not isolate scopes and meters...
But the benefits far outweighs the risks...

Nevertheless some specific faulty devices will need special
care.. for that galvanic isolated meters (BAT POWER) and
may be compatible proper generation (aka use TUBE bench tools)
will solve a lot of issues

Paul

[Electro Detective]

Add gloves, eye protection and rubber soled shoes to PKTKS setup/s above    (which roll very similar to mine  )

and it's as safe as safe can be.. 


..that only a collapsed ceiling due to plane crash, obese termites or fatass neighbors above  , earthquake, tsunami,
alien invasion/saucer crash or zombie apocalypse can stuff it up 

[nctnico]

What are people’s views on the best way to protect yourself.

I have a large isolation transformer, large variac and bulb current limiter.

What order?
Which devices?

I work on guitar amps and currently messing with valve amps. My current protection method involves discharging caps and attaching leads etc before turning the device on. Sometimes checking things with the power on is useful. It would also be helpful to protect the device as well.

What are people’s views? At the most the isolation transformer goes into the bulb limited and I have just bought a job lot of variacs.

The best way to protect yourself is to use a CAT rated differential probe when working with high voltages (including mains). I advise against the isolation transformer to create a floating mains. There are a gazillion ways to ground the circuit again. Better use a low current GFI (which you test before doing a measurement).

[cowasaki]

Thanks so far. Lots to consider. I have several variacs but only one large isolation transformer. I could make another using two transformers or buy another. Would all the equipment on the bench be ok through one isolation transformer? If so I could use my existing one which is capable of supplying 13a at mains voltage.

[PKTKS]

Thanks so far. Lots to consider. I have several variacs but only one large isolation transformer. I could make another using two transformers or buy another. Would all the equipment on the bench be ok through one isolation transformer? If so I could use my existing one which is capable of supplying 13a at mains voltage.

NO NEVER PLUG YOUR DUT ISOLATOR in your bench tools isolation unit.

Depending on what kind of devices you will work the setup will change.

For tube based devices IDEALLY you would use TUBE based scopes
and meters... kinda proper devices to suit the measures...

You will never use for example an USB scope (5V rated pretty much masx 35V)
with that sort of hardware... got it ?  match things is also important.

For SMPS last decade power ranges were more sane.. below 500W is more simple
But present days SMPS have gone insanely dangerous.

Power ratings of 1000W or 1200W are common with AMPERAGE inrush
ratings of 100A or 200A on MOBOs. The kind of ISOLATOR for that is not trivial.

As said above - differential probes are becoming more important.. but nevertheless
they are WAY TOO MUCH EXPENSIVE... unless you make a living of them..

So a couple or 3 ISOLATION UNITS for your bench - ONE SEPARATED UNIT w/a proper
VARIAC for DUTs... - should be a reasonable and affordable setup

.. last but not least - yourself protection pretty much depends on the sort
of work - being solder, HIGH VOLTAGE... and other stuff..

a PROTO BOARD with ARDUINO definitely will not need much...
while DESOLDERING OLD CRAPPY CORRODED AMPS...
will require eye and lungs and skin/nail protection..
NASTY STUFF

Paul

[BravoV]

What are people’s views? At the most the isolation transformer goes into the bulb limited and I have just bought a job lot of variacs.

My view ... as I had been thru the same path in the past using isolation transformer, bulb trick and etc, and then I realized all of these are prone to mistake when swapping or reconnecting mains wirings and etc.

As working with dangerous voltage, one mistake, say 0.01% mistake or just once, out of 99.99% correct, is enough to toast your scope, your limb or your life. Think about it, is it worth the risk ?

Consider to save money for HV differential probe, even cheap one is better than none if you do this alot.

Once you owned it, probing mains related devices will be much-much less riskier, an example a scope was probing the mains line that powered the scope it self using HV diff. probe.

[cowasaki]

I think a differential probe is likely my next purchase but everything I have I’ve had for a while. Just have my new PSUs to pay for at the weekend then that’s likely next. I’ve designed some valve based effects so quite like the idea of a HV probe. I’ve been looking for a suitable scope for a while. I currently have a decent spec UNI-T scope which was ideal for the computers and other stuff. I have a novascope which only cost £10 which I use for audio as I is very quick to setup and adjust. I see mr carlsons lab and the number of valve scopes he gets but not sure what happened to them all in the uk!

[PKTKS]

(..)
As working with dangerous voltage, one mistake, say 0.01% mistake or just once, out of 99.99% correct, is enough to toast your scope, your limb or your life. Think about it, is it worth the risk ?

Consider to save money for HV differential probe, even cheap one is better than none if you do this alot.
(..)

True but indeed this risk is UNAVOIDABLE.

Even having ALL OF THIS STUFF... all.. put ISOLATOR VARIAC BULB..
and use DIFFERENTIAL PROBE...

We are still  prone to touch (with the probes or fingers ) parts which
should not be touched while servicing..

A small fraction of a second is enough to spark and TOAST EVERYTHING.
With a simple probe in the wrong place.

Same with the hand and fingers.. touching some parts is necessary
and BEING GROUNDED (pulse ground) may be deadly.

So always consider if the setup is really safe per si - regardless the measures
This is the hard part.. and mistakes still happen...

Part of the thing.
Experience does help however it will not save you from mistakes

Paul

[BravoV]

(..)
As working with dangerous voltage, one mistake, say 0.01% mistake or just once, out of 99.99% correct, is enough to toast your scope, your limb or your life. Think about it, is it worth the risk ?

Consider to save money for HV differential probe, even cheap one is better than none if you do this alot.
(..)

True but indeed this risk is UNAVOIDABLE.

Even having ALL OF THIS STUFF... all.. put ISOLATOR VARIAC BULB..
and use DIFFERENTIAL PROBE...

We are still  prone to touch (with the probes or fingers ) parts which
should not be touched while servicing..

A small fraction of a second is enough to spark and TOAST EVERYTHING.
With a simple probe in the wrong place.

Same with the hand and fingers.. touching some parts is necessary
and BEING GROUNDED (pulse ground) may be deadly.

So always consider if the setup is really safe per si - regardless the measures
This is the hard part.. and mistakes still happen...

Part of the thing.
Experience does help however it will not save you from mistakes

Paul

Yeah, example of touching the tiny portion of the exposed metal at the probe tips ... both hands ... mains voltage connected  ... thats different story, no matter how good the protection is, it wont help.

[nctnico]

Thanks so far. Lots to consider. I have several variacs but only one large isolation transformer. I could make another using two transformers or buy another. Would all the equipment on the bench be ok through one isolation transformer? If so I could use my existing one which is capable of supplying 13a at mains voltage.

NO NEVER PLUG YOUR DUT ISOLATOR in your bench tools isolation unit.

Depending on what kind of devices you will work the setup will change.

For tube based devices IDEALLY you would use TUBE based scopes
and meters... kinda proper devices to suit the measures...

You will never use for example an USB scope (5V rated pretty much masx 35V)
with that sort of hardware... got it ?  match things is also important.

As said above - differential probes are becoming more important.. but nevertheless
they are WAY TOO MUCH EXPENSIVE... unless you make a living of them..

So a couple or 3 ISOLATION UNITS for your bench - ONE SEPARATED UNIT w/a proper
VARIAC for DUTs... - should be a reasonable and affordable setup

Bad advise. Differential probes cost less than an isolation transformer nowadays (MicSig sells a very economic one). Using isolation transformers is just dangerous. There are too many ways to ground stuff. Better keep everything grounded while protected with a low current GFI. That way you can minimise the danger area to the DUT and the probe leads which is much easier to keep an overview on and thus have less chances of a mistake.

[madires]

I advise against the isolation transformer to create a floating mains. There are a gazillion ways to ground the circuit again. Better use a low current GFI (which you test before doing a measurement).

I'd prefer an isolation transformer when working on a hot chassis.

[madires]

Same with the hand and fingers.. touching some parts is necessary
and BEING GROUNDED (pulse ground) may be deadly.

Rubber gloves

[cowasaki]

My isolation transformer is 3.6Kv but no current limiting. I have the bulb limiter plugged into the isolator. There is a 13a fuse in the lead to the transformer and another between the transformer into the limiter. I could get an isolation transformer for a single device and swap it as required if that would help WITH the dif probe!

[cowasaki]

And I have rubber gloves. The floor is wooden and carpeted.

[PKTKS]

Bad advise. Differential probes cost less than an isolation transformer nowadays (MicSig sells a very economic one). Using isolation transformers is just dangerous. There are too many ways to ground stuff. Better keep everything grounded while protected with a low current GFI. That way you can minimise the danger area to the DUT and the probe leads which is much easier to keep an overview on and thus have less chances of a mistake.

NO not here in Brazil
and may be other places and other budgets.

Almost 100% stuff in Brazil is now IMPORTED.
TAXES OF EVERYTHING ... are pretty much 100% - AT LEAST!
sometimes may be more due to extra shipping costs

Prices are for sure the DOUBLE at least may be 3x times
EVERY STUFF YOU SEE on EBAY ALIX and BANGOOD...

3x times of EVERYTHING is not a good bottom line to live with

Paul

[PKTKS]

My isolation transformer is 3.6Kv but no current limiting. I have the bulb limiter plugged into the isolator. There is a 13a fuse in the lead to the transformer and another between the transformer into the limiter. I could get an isolation transformer for a single device and swap it as required if that would help WITH the dif probe!

For costing issues I have replaced the FRONT END TRIPPING FUSE
with a zing-ear ZE-800

http://www.zingear.com/e/proDetail.php?id=6735&cateid=29571

Several advantages and so far so good every issue was
nicely handled. The real fuses are on the secondary side

Paul

[AVGresponding]

OP is from the UK, not Brazil.

You most likely have an RCD, maybe even RCBO protected mains. These trip at 30mA earth fault currents. You can buy ones that trip at lower currents.

In my experience, isolation transformers and variacs have their place, but can lead to complacency. To be absolutely, 100% clear:

AN ISOLATION TRANSFORMER WILL NOT PROTECT YOU FROM ELECTRIC SHOCK IF YOU TOUCH BOTH OUTPUTS SIMULTANEOUSLY.

Its primary function is to prevent a line-earth short when connecting two line powered devices, ie probing your DUT with your scope.
If you touch both outputs (call them Line and Neutral if you like), it will happily cook your arse with the full current it can supply. Since I believe you mentioned 3.6 KVA, which is 15 amps at 240V. Would you like fries with that human-burger?

By all means use an isolation tranny and variac to protect your DUT and scope, but run your scope off an RCD/RCBO protected, earthed supply, to protect YOU.

[cowasaki]

Thanks. I think that that resettable fuse looks good. Any other alternatives?

[AVGresponding]

Limit the self-tanning effect with one of these.

[PKTKS]

Thanks. I think that that resettable fuse looks good. Any other alternatives?

nop haven't seen better for this purpose.

I can find them easily right here or even from AliEx.

They are cheap (cheaper than equivalent fuses) and hassle free
with BONUS .. they have the PANEL mounting already

Combine them with a regular NEON you have a cost effective
tripping wired on the mains front end

Save your money for the secondary side.. more complex.
piece of cake
Paul

[nctnico]

Bad advise. Differential probes cost less than an isolation transformer nowadays (MicSig sells a very economic one). Using isolation transformers is just dangerous. There are too many ways to ground stuff. Better keep everything grounded while protected with a low current GFI. That way you can minimise the danger area to the DUT and the probe leads which is much easier to keep an overview on and thus have less chances of a mistake.

NO not here in Brazil
and may be other places and other budgets.

Almost 100% stuff in Brazil is now IMPORTED.
TAXES OF EVERYTHING ... are pretty much 100% - AT LEAST!

Your family will agree that it is better to pay 100% tax rather than taking a chance to die. Besides that an isolation transformer will be imported too so the tax also applies.

[nctnico]

Besides that... how about powering the amplifier using a lab power supply which can provide the 300V (or so). Lab power supplies have very well behaving current limiting and the fancier ones will discharge the output when the output is switched off.

[PKTKS]

(..)
Your family will agree that it is better to pay 100% tax rather than taking a chance to die. Besides that an isolation transformer will be imported too so the tax also applies.

 
I started my journey in electronics way back in early 70s

By that time I had obsessive fixation on a TELEFUNKEN B&W TV
ALL TUBES which I have spent significant time watching cartoons
and crappy stuff...

From time to time it went dead .. technicians were rare and when
they come to "FIX" I was almost inside the tube watching...

Well guess what? Very soon the tech was no longer needed
and I have lost the count how many times I zapped myself on
that smelling hot tubes.. about 8 tubes with 400 ~600 DC volts
almost 80C at least..

Any usual child would have just gave up that pile of hazard away..
Some folks instead thinks that is a good laugh - and for my case..
Those 600V DC zaps just made me more and more interested..

Some neurons I am sure are lost.. but as soon as the cartoons
appeared again they went back..

Well  70s  TELEFUNKEN  B&W TV was indeed quite a starting ride.

Today a 1200W SMPS or 3000W inverter does not scary that much
My neurons healed watching cartoons....

Paul