Hot Patching
- Thread starterMayhem
- Start date
Footer4321 said:
On the right track now.
Diarmuid said:
Well the context in which I have heard the term is in regards to plugging into a live circuit, so this would also include a dimmer.
To be honest with you – I believe it to be more common in the US than is Australia or the UK, as out power outlets have switches on them, where the US ones do not (well not that I have seen). If the unit being plugged in has a power switch it is not a problem (but still not good practice). But grabbing a high wattage light and plugging it into a hot outlet can change your outlook on the day.
Think about the B grade horror movies where there is an old style cam switch (the big old open contact lever ones) and recall what happens as the two contacts come together. Now, imagine that wrapped in fairly thin plastic with your hands griping onto it. Ok – so you have to use your imagination a little but that is what is happening inside of the plug.
"Even a single power lead with a 650W lantern running on the end will cause a decent spark inside the socket at the point of disconnection. Each time this happens, the socket and the pins get damaged. This damage causes resistance at the join – and given enough damage, that could lead to a fire. If you have ever seen someone disconnect a three phase connection under load, it is the same effect, but multiplied significantly.
That kind of disconnection will ‘blacken’ the interior of the socket, and cause it to fail its next electrical tagging. It could even potentially ‘jump out’ and get you depending on the amount of load, age/wear of the connection etc." http://www.juliusmedia.com/cxweb/article.asp?ID=446
Electricity can jump 1cm for every 10 000 volts in dry air. When a plug is hot patched to a socket, at a point 2.4mm from contact [240V parts of the world], an arc occurs between the plug & socket. This will then lead to a buildup of carbon, you have probably seen this on plugs before. This carbon buildup introduces a higher resistance into the connection and if repeated, this will eventually lead to an intermittent or faulty connection.
It is worth noting that the design of some connectors prevents or at least lessens the impacts of disconnection under load. Speakon connector being an example. Similarly, connectors such as Neutrik Powercon must not be disconnected under load as they are not rated for that.
Consider also that while we may be more aware of arcing in connectors, every time we flick a switch, there is a small amount of arcing occurring. This is one reason why switches can fail. Older switches can get to a point where they are not disconnecting properly and a blue arcing can be seen even through the plastic of the housing. If this occurs, it is replacement time.
It is interesting to note that circuit breakers normally contain plates to stop the ionisation of gas & arcing when they disconnect the load.
If the connection is through a dimmer and the dimmer is at a low level, the effect will not be as profound but will still occur, hence why one should not hot patch.
That kind of disconnection will ‘blacken’ the interior of the socket, and cause it to fail its next electrical tagging. It could even potentially ‘jump out’ and get you depending on the amount of load, age/wear of the connection etc." http://www.juliusmedia.com/cxweb/article.asp?ID=446
Electricity can jump 1cm for every 10 000 volts in dry air. When a plug is hot patched to a socket, at a point 2.4mm from contact [240V parts of the world], an arc occurs between the plug & socket. This will then lead to a buildup of carbon, you have probably seen this on plugs before. This carbon buildup introduces a higher resistance into the connection and if repeated, this will eventually lead to an intermittent or faulty connection.
It is worth noting that the design of some connectors prevents or at least lessens the impacts of disconnection under load. Speakon connector being an example. Similarly, connectors such as Neutrik Powercon must not be disconnected under load as they are not rated for that.
Consider also that while we may be more aware of arcing in connectors, every time we flick a switch, there is a small amount of arcing occurring. This is one reason why switches can fail. Older switches can get to a point where they are not disconnecting properly and a blue arcing can be seen even through the plastic of the housing. If this occurs, it is replacement time.
It is interesting to note that circuit breakers normally contain plates to stop the ionisation of gas & arcing when they disconnect the load.
If the connection is through a dimmer and the dimmer is at a low level, the effect will not be as profound but will still occur, hence why one should not hot patch.
Chris15 said:
Well done. However, if you have seen someone disconnect a three phase lead under load, I hope that you beat them over the head with the plug. Not only is it a good way to remover yourself from the gene pool but wrecks the springs in the sockets and you cannot buy replacements any more. There is another wasted $200+
The arcing and jumping that you refer to when disconnecting underload also occurs when connecting under load.
The other important factor to consider is that hot patching is often done to test a (potentially) faulty piece of equipment.
Lets go back to the 650W Fresnel and imagine that you just pulled a pair from the rig because they didn’t work and threw the breaker on the dimmer (plugged into the same circuit). So, you grab one and plug it in to a live feed.
What would happen if the lamp base had failed creating a dead short and you are now holding the plug in one hand and about to stick it into the end of an extension lead that you are holding in your other hand?
Mayhem said:
One hopes that one has an operational RCD / GFCI and /or defibrillator. What will happen is that there will be the arcing seen normally, but since there is a short and thus that arc will not have any limit imposed upon it as to the amount of current that will be drawn. Given this, it should not be long before you trip your circuit breaker / fuse but in the mean time, you have probably sustained a reasonable electric shock and hopefully have worked out that it was not a safe thing to do in the first place.
rustystuff
Member
When I was in high school, (back before the Earth cooled), we would occaisionally have a show that required more specials than we had available dimmers. The patch panel resembled an old fashioned telephone operator's panel, with plugs that pulled out and were plugged into receptacles. We alsways made sure the dimmer handle was at "0" before anything ws re-plugged. Admittedly not the best way; but it was making the best of a bad situation.
Would you get a electric shock from the plug, as it was shorted, and (i dont know the science behind this) but would that cause the current to be different to what it would of been, if it was flowing through the lamp, i.e. stronger or more intense and as such cause the spark inside the socket/plug to be larger, and thus have a greater chance of getting you?
Also, surely hot patching is quite a bad method of testing a fixture, for example if the lamp hadnt blown, but something in the Internally Wired Bar was wrong, is it not possible that by hot patching the light, without pre-heating the filament, the lamp would then blow anyway.
Also, surely hot patching is quite a bad method of testing a fixture, for example if the lamp hadnt blown, but something in the Internally Wired Bar was wrong, is it not possible that by hot patching the light, without pre-heating the filament, the lamp would then blow anyway.
Radman
Well-Known Member
So wait, black is ground? 
This is one more reason someone should invent wireless power cables. Or a connector with a switch that must be thrown to connect/disconnect. Probably wouldn't be viable for cams though, too much current! I admit at times I do hot patch lights sometimes, but then again I never have anyone helping me, so it would not fit into my schedule if I had to go to the board every time I plugged something in.
Come to think of it, outlets that aren't on dimmers are generally always hot, so that's hot patching every time you plug/unplug anything. Scary...
This is one more reason someone should invent wireless power cables. Or a connector with a switch that must be thrown to connect/disconnect. Probably wouldn't be viable for cams though, too much current! I admit at times I do hot patch lights sometimes, but then again I never have anyone helping me, so it would not fit into my schedule if I had to go to the board every time I plugged something in.
Come to think of it, outlets that aren't on dimmers are generally always hot, so that's hot patching every time you plug/unplug anything. Scary...
my thought with the spagetti board patch is that if the dimmer is at 0 then there is no problem with patching durring a show like that. i do not see it as an issue.
question: could this also cause a breaker to wear out? I worked at a pool and i told them the breaker was bad because if it was off for a while it would not always flip back on with out continualy flipping it. the breaker is used as a on off switch for the main pump. it is turned off at least once a day to clean the strainer basket thingy.
question: could this also cause a breaker to wear out? I worked at a pool and i told them the breaker was bad because if it was off for a while it would not always flip back on with out continualy flipping it. the breaker is used as a on off switch for the main pump. it is turned off at least once a day to clean the strainer basket thingy.
Hot patching is a good way to blow a lamp and I think someone already pointed out that when a lamp fails, it quite often does it when being turned on.
The risk of shock or even other damage caused by a large current draw in the material in your hands can cause other painful injuries as well.
There are plenty of connectors that have switches on them and they certainly in common use in Australia and the UK and several other countries that I have visited. It seems that the US hasn’t embraced the need for them. In my workshop all the wall receptacles have switches built into them and all circuits are breakered and protected by a RCD. I even have a pendant receptacle with a switch on it hanging over an island bench.
Having said this – how hard would it be to make up a test bench power supply that not only had a switch on it, but also a RCD and a breaker or fuse?
I don’t think that wireless power would solve the problem as some bright spark would find a way to use it in an unsafe manner!
Koncept - yep, wear and tear will do that and it is not advisable to use a breaker as a switch.
The risk of shock or even other damage caused by a large current draw in the material in your hands can cause other painful injuries as well.
There are plenty of connectors that have switches on them and they certainly in common use in Australia and the UK and several other countries that I have visited. It seems that the US hasn’t embraced the need for them. In my workshop all the wall receptacles have switches built into them and all circuits are breakered and protected by a RCD. I even have a pendant receptacle with a switch on it hanging over an island bench.
Having said this – how hard would it be to make up a test bench power supply that not only had a switch on it, but also a RCD and a breaker or fuse?
I don’t think that wireless power would solve the problem as some bright spark would find a way to use it in an unsafe manner!
Koncept - yep, wear and tear will do that and it is not advisable to use a breaker as a switch.
Diarmuid said:
In my opinion, yes. The lamp filament has a given resistance which will change slightly as heated but for this, remains a constant. Power = volts squared over resistance. Thus, with the standard mains voltage, the different resistances of the filaments will regulate the brightness of the lamp. Say, for instance, you have a 250W lamp and your mains voltage is 250 volts. P = V x V / R. Rearranging this, R = V x V / P. Now for the above example, R = 250 x 250 / 250 = 250 ohms. In this case a current of 1 amp will flow.
If there is a short circuit, the resistance is much lower, say 1 ohm or less, at 1 ohm, 250 volts, 250 amps will flow. You can see the difference in current. 250 amps will produce quite a spark. It will also trip a circuit breaker / fuse pretty quickly.
In response to the second part, have you noticed that if a lamp is going to blow in your house, 9/10 times it will be when you switch it on...
Radman said:
Some nice folks down here in Australia have thought of you. Australian 3 phase sockets can be ordered with a mechanical interlink such that you have to turn off the switch to be able to insert or remove a plug. Have to specially order them but they are available from Clipsal.
Do US dimmers not have circuit breakers on the front panel. I can see no justification for plugging in hot to an Australian portable dimmer pack such as the Jands HP12. Flick the breaker on the front, connect the load, flick the breaker back on.
Lightingguy32
Active Member
Lightingguy32 said:
Now we need to remember that even though the DMX output might be 00, many dimmers have a preheat setting so that there is a small amount of power going through the lamp so that lamps don't blow as quickly, so this can still cause arcing, since with most dimmers, the full voltage is there, just not all the time, so effectively there is less voltage.
Lightingguy32
Active Member
i disagree completely. we were doing a show and needed little lights like 3 watts so we wired about 4 of them up like we wanted to give us a 12 watt load. on a 2.4kv dimmer they lit right up bc there was no ghost load. and this was with the board set to 00 and off...on newer dimmer racks with a processor you can change settings directly on the rack and override the settings on the board.
Sorry, But I have to disagree. More often than not, the preheat is a setting on the dimmer rather than the desk. Let me pose this question: what use is the preheat if it turns off after a few minutes? I thought that the idea of preheat was so that the filament was warm so that if you say flashed the lamp, the filament did not have to warm up and so was less likely to sustain damage. I recall that triacs and dimmer circuits have limits. We know that they cannot go all the way to 180 degrees. Hence one of the reasons that dimmers (except in some very specific cases) are not suitable for supplying clean power. Those specific cases are where there is a setting that changes it so that it activates a relay, bypassing the triacs etc. and chokes and all that. I also recall there it is a point, maybe 5 degrees which the dimmer can't go below.
This is why dimmers have marked minimum loads. The preheat and the lower limitation of the switching mean that there is still sufficient power to light up small loads.
I certainly did not mean to imply otherwise. I apologise if I did.
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