The boring bit..... H&S

[Corky]

Hi every one, this is my first post so sorry if i make any mistakes, im doing a level three Btec at college in the uk, i recieved a question asking for H&S precautions using a high voltage electronics circuit which i answered with the standard, circuit breakers, rubber matting etc and also some answers like dehumidify the room too (I was trying to cover all aspects) but the result came back fail and i needed to add more specific safety precautions for Electronic circuits and not electrical circuits, after doing a fair bit of research im still in the same posistion, does anyone have any advise on what i should be looking for or any ideas to help me meet the criteria? Thankyou

 

[Ian Rogers]

I hate Health and Safety.... Remember what it used to be called.... Common sense!!!!

I would say Observation... Identify the high voltage part and take precautions, remember to wear a grounding band on your wrist..

 

[Corky]

I spoke to my instructor about the grounded band but he said i wouldnt use it if i was working on high voltage (400v in the asignment) he also said i wouldnt wear gloves or glasses as they would get in the way and make life hard during the work. is this an accurate comment?

 

[KeepItSimpleStupid]

Well, I worked on a 15 kV 1A power supply with a mains input of 208 3 phase at 60 A and 100 kV supply at 0.1A and an RF tube xmitter with a 3 kV supply in it.

Grounding stick - yes. One hand in pocket - yes. Make some measurement connections with power off - yes. Gloves - No. Safety glasses - Yes (Normal for being in the room).

Then when I changed a light bulb (2x per year): Gloves - no fingerprints allowed. Face shield - lamp pressurized to 15 atm. Heavy padded shirt - same reason. Lab coat. No one else in the room. Sign on door - no entry.

Arc Flash Hazards is another area for PPE.

 

[KeepItSimpleStupid]

Gloves and glasses is not an accurate comment. I might not use gloves if it was 400 V at 10 mA, but might if the box was 400 V at 100 Amps. I don't know where I would draw the line.

Even changing a car battery can be hazardous. Watch a screwdriver get across the terminals. Like 12V @ 600 A for a few seconds. Longer could cause an explosion. Battery acid could splash in your face.

So, Job Hazard Analysis and an accompanied SOP (Standard Operating Procedure) is an effective tool to do in a workplace followed by Emergency Procedures.

 

[Nigel Goodwin]

remember to wear a grounding band on your wrist..

Why on earth would you want a wrist band?, it's providing no protection for YOU at all, and can only lower your protection level.

H&S is generally total crap, with most supposed H&S restrictions nothing of the kind - but for his assignment it's a question of having paid attention in class, they are looking to check he's been paying attention!.

 

[Corky]

i have recieved my work back with " but what precautions MUST you take to keep you safe while working on 'LIVE' equiment. is he getting to the point that i need to switch the equipment off he said to me personally that i need to add more things like circuit breakers but ive done research and i couldnt find anything similar to circuit breakers which would work in this. cheers guys

 

[Corky]

Why on earth would you want a wrist band?, it's providing no protection for YOU at all, and can only lower your protection level.

H&S is generally total crap, with most supposed H&S restrictions nothing of the kind - but for his assignment it's a question of having paid attention in class, they are looking to check he's been paying attention!.

I do pay alot of attension im generally really interested in this and i took a big salary drop to get on this courseto enjoy my job in the future i wrote everything he said to write yet it wasnt included i think he may have made a mistake but i dont mind finding this stuff out for myself im just not sure where to look,

 

[Ian Rogers]

Why on earth would you want a wrist band?, it's providing no protection for YOU at all, and can only lower your protection level.

I would rather the current ground through my wrist than any other path!! I have had my share of 240v though the hand!!

 

[JimB]

H&S precautions using a high voltage electronics circuit

A rather vague definition.
What constitutes High Voltage?
What constitutes Electronics?

To a "light current" guy like my self, high voltage is something which will hurt you, whereas the "power" guys definition may be a voltage greater than 1000 volts.

Similarly, to me electronics is something with transistors and ICs, to the power guy it may be BIG thyristors, triacs and diodes.

A couple of different examples from my own experience:

In the workshop repairing an oscilloscope with CRT.
Can the workbench support the weight of the equipment under test (EUT) and the associated test equipment?
Can anything fall off the bench?
Can the EUT be safely moved for access to the various internal circuits?
Do I have enough room to work safely and move away from the bench if things go wrong?
If things go wrong, how do I switch off the power to the bench?
Where are the high voltages in the EUT?
The mains power
The high voltages ( say +/- 200 to 300 volts)
The EHT for the PDA (say 10 to 15kV)
Are the test equipments suitable for the voltages I am about to measure?
Is the service manual/schematic for the EUT available?

At a process plant/oil refinery/offshore oil production platform, working inside a cabinet of control equipment.
Do I have authority to work on this?
Are the Permits to Work open?
What can happen if I do something wrong?
Will the process stop?
Will there be a release of hydrocarbons or chemicals?
Will some machinery start unexpectedly?
Am I working in the correct cabinet?
Where is the mains supply, how do I isolate it if necessary?
I am just working on the low voltage (24volt) circuits, but is there a possibility that I can trip the 24v power supplies?


Not exhaustive lists, but these are the things which have affected me in the past.


From some of the comment by the OP about his instructor, I cannot help but think that this is a case of the blind leading the blind.
Has the instructor ever done this stuff for real, or is he just a "gob on a stick" ?

JimB

 

[JimB]

Why on earth would you want a wrist band?, it's providing no protection for YOU at all, and can only lower your protection level.

I would rather the current ground through my wrist than any other path!! I have had my share of 240v though the hand!!

Ian, the purpose of the wrist strap it to prevent the build-up of static charge on YOU, so that you do not cause ESD damage when you touch ESD sensitive components.

A correctly designed and built wrist strap assembly should have a built-in 1Meg Ohm resistor.
If you are touching 240v, the current through the strap should not exceed 0.24mA, a very mild tickle.
If your other hand is grasping an earthed object, the wrist strap will make no difference and you will get one hell of a belt!

JimB

 

[Corky]

Hi JimB cheers for the attempt to answer with a pretty poor description of my question, sorry about that, my question asks:
Your supervisor at work has asked you to carry out repairs on a high voltage inverter circuit. The voltage will be in excess of 500v. what safety precautions would you have to carry out when testing the circuit?
hope this helps

cheers again

 

[JimB]

Dale,

Again the information is lacking.

Is this a small stand alone inverter which is on the bench in the workshop?
If it is, then my guidelines for the oscilloscope would be applicable.

or

Is it a big inverter/UPS in a whole room of its own, powering the instrumentation in a process plant?
If it is, then my guidelines for a process control cabinet would apply, plus relevant precautions for BIG POWER DC and AC.

JimB

 

[ronsimpson]

Gloves (insulated)
boots (insulated)
one hand in pocket. Don't touch ground with other hand. (no ground strap)
Insulated tools.
Meter/tester to check if wires are live.
Al wise think wires are live even when you know they are not.
Glasses
Have a buddy near by. Who can phone for help and do CPR.
We have tied a rope to a person encase we need to pull then off a wire.
I know several people that say something just before reaching for high voltage. "Oh God" Might help. Does not hurt.

 

[Ian Rogers]

Ian, the purpose of the wrist strap it to prevent the build-up of static charge on YOU, so that you do not cause ESD damage when you touch ESD sensitive components.

Yes I know the reason for the wrist band... If you touch a 240v supply whilst your other hand is on ground then you'll feel it!! If your hand that accidentally touches the supply has the wrist strap then you will only feel it in your hand even if you are touching ground with the other hand..... Through the arms across the torso isn't the best electric shock to get!!

 

[JimB]

If your hand that accidentally touches the supply has the wrist strap then you will only feel it in your hand even if you are touching ground with the other hand

I have to totally disagree with that statement.

10k Ohms in parallel with 1M Ohms, apply volts, which one carries the most current?

JimB

 

[Nigel Goodwin]

Yes I know the reason for the wrist band... If you touch a 240v supply whilst your other hand is on ground then you'll feel it!! If your hand that accidentally touches the supply has the wrist strap then you will only feel it in your hand even if you are touching ground with the other hand..... Through the arms across the torso isn't the best electric shock to get!!

Sorry Ian, but you are sadly mistaken - assuming it's a normal ESD wristband then it only has a high resistance to earth to bleed off any static charge - but if it's a direct connection to earth then it would be a VERY serious safety hazard, and would certainly fail any H&S checks.

 

[Ian Rogers]

OK! Point taken...... Just sit on a large rubber mat!

 

[Corky]

the answer the instructor was looking for was use an isolating transformer

 

[ericgibbs]

the answer the instructor was looking for was use an isolating transformer

hi Dale,
I would suggest you change instructors.!

The ONLY potential electrical hazard a mains isolating transformer will 'protect' you from is getting yourself across mains Line to Earth, it will NOT protect you from hazards from on board high voltages or receiving electrical shocks from across the secondary of the isolating transformer.

E