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Old 07-13-2009, 08:25 AM   #11
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Default Re: A lesson about resistance learned the hard way

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Old 07-13-2009, 08:47 AM   #12
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Default Re: A lesson about resistance learned the hard way

Re: A lesson about resistance learned the hard way

Should be...

Re: A lesson about inductance learned the hard way

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Old 07-13-2009, 11:28 AM   #13
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Default Re: A lesson about resistance learned the hard way

Quote:
Originally Posted by berry120 View Post
Was your (or whoever it was) immediate reaction not "crap we've clearly plugged too many computers into one coiled up extension reel, we better check some things through before doing that again" instead of "ah well, these things happen, let's go grab another extension cord"?! If you're pulling power close to the limit of a 13A socket, then you should be using uncoiled cable rated to 13A or more... it's worth checking these things through!
It actually was, "crap we've clearly plugged too many computers into one coiled up extension reel"

Somebody left with one of their computers, as well after that happened, because it wouldn't get past the post screen after it got unplugged.
We were going to feel the other one to be sure that it didn't get warm after that happened.
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Old 07-13-2009, 12:11 PM   #14
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Default Re: A lesson about resistance learned the hard way

Considering you could be drawing around 15 Amps through that cord your lucky it lasted at all
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Old 07-13-2009, 06:57 PM   #15
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Default Re: A lesson about resistance learned the hard way

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That's nuts, when we have an lan party, each computer gets their out outlet and power strip.
But wouldn't you have to run the cords all over the house to really have any effect?
I mean yes the lead cords and power strips are good but plugging them all into different outlets.. I can see SORT of working.. But usually the circuit breaker is set up for rooms. Thus the reason why you would have to run them all over the house.


EDIT: Yes plugging them into different outlets would release pressure on the wires leading to the outlets. But they all lead to the same place.. Usually to one wire that leads to the breaker.. Right?
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Old 07-13-2009, 07:38 PM   #16
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Default Re: A lesson about resistance learned the hard way

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But wouldn't you have to run the cords all over the house to really have any effect?
I mean yes the lead cords and power strips are good but plugging them all into different outlets.. I can see SORT of working.. But usually the circuit breaker is set up for rooms. Thus the reason why you would have to run them all over the house.


EDIT: Yes plugging them into different outlets would release pressure on the wires leading to the outlets. But they all lead to the same place.. Usually to one wire that leads to the breaker.. Right?
Note that I'm in the UK, so the examples I use may seem odd to other standards. The principles however should be the same.

There's restrictions at several levels that need to be looked at here - the first is how much current the cable from the socket can safely carry in its state. In this case it clearly wasn't anywhere near good enough, perhaps it would've still packed up if it was uncoiled, we can't know without knowing details of the cable. All of the extension leads I make have cable rated at 16A or above - yes it's a bit overkill when I can only draw 13A max from a single socket, but I require them occasionally when 16A plugs and supplies are in use. That way I can simply change the plug at the end without worrying about whether the cable will melt if someone draws a bit too much current through it!

As long as you're well within all these limits (and any others that might exist, I'm not saying that's an exhaustive list!) then you're fine. So if your upstairs ring main has a limit of 32A and you're drawing 25A worth of stuff, you'd need to run it from 2 different plug sockets that weren't part of the same double socket, but you could still use the same ring main quite safely. If you had 35A worth of stuff for whatever reason, it's a different story and yes you would need to start running cables all over the house!

Beyond this, there's the limit of each socket (13A max), the limit of each double socket (usually around 20A between the two sockets - people tend to forget this but very few double sockets are rated to supply 13A to each socket at once!) the limit on your ring main (often 16A or 32A) and finally the limit of the total current coming into the house. If you blow that last one then you're doing something seriously seriously wrong!

Yes, in some cases you'll know when you've overrated something. If you draw more than 13A from a socket, the fuse should blow. If you draw more than 32A from a 32A ring main, the MCB on the ring main should trip. But it's very bad practice to rely on these instead of doing your own calculations - they should be seen as precautionary measures only in case you screw up. Also, some weaknesses in the chain (such as the 20A limit from a double plug socket and the above under-rated cable configuration) won't be protected in any way at all, and could cause serious damage, start a fire, or worse kill someone.

I know that sounds melodramatic, but electricity can be lethal even on a domestic level if people mess around with it. I for one would always advise that when you're not sure over something, check it with the relevant calculations, double check, and if you're still not sure get someone who is! This isn't meant as a go at anyone, I'm genuinally glad no-one was hurt and that you learnt your lesson I just hope this goes down as a reminder to everyone that reads it!
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Old 07-13-2009, 10:27 PM   #17
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Default Re: A lesson about resistance learned the hard way

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Originally Posted by berry120 View Post
Note that I'm in the UK, so the examples I use may seem odd to other standards. The principles however should be the same.

There's restrictions at several levels that need to be looked at here - the first is how much current the cable from the socket can safely carry in its state. In this case it clearly wasn't anywhere near good enough, perhaps it would've still packed up if it was uncoiled, we can't know without knowing details of the cable. All of the extension leads I make have cable rated at 16A or above - yes it's a bit overkill when I can only draw 13A max from a single socket, but I require them occasionally when 16A plugs and supplies are in use. That way I can simply change the plug at the end without worrying about whether the cable will melt if someone draws a bit too much current through it!

As long as you're well within all these limits (and any others that might exist, I'm not saying that's an exhaustive list!) then you're fine. So if your upstairs ring main has a limit of 32A and you're drawing 25A worth of stuff, you'd need to run it from 2 different plug sockets that weren't part of the same double socket, but you could still use the same ring main quite safely. If you had 35A worth of stuff for whatever reason, it's a different story and yes you would need to start running cables all over the house!

Beyond this, there's the limit of each socket (13A max), the limit of each double socket (usually around 20A between the two sockets - people tend to forget this but very few double sockets are rated to supply 13A to each socket at once!) the limit on your ring main (often 16A or 32A) and finally the limit of the total current coming into the house. If you blow that last one then you're doing something seriously seriously wrong!

Yes, in some cases you'll know when you've overrated something. If you draw more than 13A from a socket, the fuse should blow. If you draw more than 32A from a 32A ring main, the MCB on the ring main should trip. But it's very bad practice to rely on these instead of doing your own calculations - they should be seen as precautionary measures only in case you screw up. Also, some weaknesses in the chain (such as the 20A limit from a double plug socket and the above under-rated cable configuration) won't be protected in any way at all, and could cause serious damage, start a fire, or worse kill someone.

I know that sounds melodramatic, but electricity can be lethal even on a domestic level if people mess around with it. I for one would always advise that when you're not sure over something, check it with the relevant calculations, double check, and if you're still not sure get someone who is! This isn't meant as a go at anyone, I'm genuinally glad no-one was hurt and that you learnt your lesson I just hope this goes down as a reminder to everyone that reads it!
Dude you really seem to know your electricity, this is twice now you have answered on the same subject.

Thank you for the information!
By any chance would you happen to know the average amount of volts/amps/watts a average computer pulls?
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Old 07-13-2009, 10:34 PM   #18
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Default Re: A lesson about resistance learned the hard way

There should be a rating on the back of your power supply. Just use this calculator to convert watts to amps.

http://www.jobsite-generators.com/po...lculators.html
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Old 07-13-2009, 11:04 PM   #19
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Default Re: A lesson about resistance learned the hard way

Thanks for your posts, berry120.

I have been zapped by 120V three times. One can never been careful enough.


Quote:
Originally Posted by vampist View Post
But wouldn't you have to run the cords all over the house to really have any effect?
I mean yes the lead cords and power strips are good but plugging them all into different outlets.. I can see SORT of working.. But usually the circuit breaker is set up for rooms. Thus the reason why you would have to run them all over the house.


EDIT: Yes plugging them into different outlets would release pressure on the wires leading to the outlets. But they all lead to the same place.. Usually to one wire that leads to the breaker.. Right?
With 16 computers, yes, you are a little limited.

There were 10 in that room, 6 in the next room


Quote:
Originally Posted by 01001010 View Post
There should be a rating on the back of your power supply. Just use this calculator to convert watts to amps.

http://www.jobsite-generators.com/po...lculators.html
Yeah, but the computers, unless you have an overdraw (bad or insufficient PSU) are going to use less than the rated value.

I find it easier to just take the watts and just divide by 120.
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Old 07-13-2009, 11:31 PM   #20
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Default Re: A lesson about resistance learned the hard way

teh,, I'm getting dual 20A sockets in my room. I dun like running all my current stuff on a 15...but it has to do for now.

Why...again...do you have 16 computers?
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