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Heat buildup in wiring

T

Terry

Jan 1, 1970
0
Hello:

Just wanted to get the general opinions on the following that was
being discussed:

The statement:

30 amps will develop 2 1/4 times more heat than 20 amps in a conductor

The data to backup the claim:

Most of us know that developed power is the product of the voltage and
current, but voltage is equal to the current multiplied by the
resistance, Hence:

P=VI
V=IR

Substituting:
P=(IR)I
P=I(squared)R

The resistance for the conductor hasn't changed but the current has
changed from 20A to 30A. 30 is 20(1.5):

P=(1.5)(squared)R
1.5 (squared) = 2.25
P=2.25R


To me this is a wee bit simplistic, it doesn't take into consideration
size of conductor, ambient temperature, length of run etc...
 
D

daestrom

Jan 1, 1970
0
Terry said:
Hello:

Just wanted to get the general opinions on the following that was
being discussed:

The statement:

30 amps will develop 2 1/4 times more heat than 20 amps in a conductor

The data to backup the claim:

Most of us know that developed power is the product of the voltage and
current, but voltage is equal to the current multiplied by the
resistance, Hence:

P=VI
V=IR

Substituting:
P=(IR)I
P=I(squared)R

The resistance for the conductor hasn't changed but the current has
changed from 20A to 30A. 30 is 20(1.5):

P=(1.5)(squared)R
1.5 (squared) = 2.25
P=2.25R


To me this is a wee bit simplistic, it doesn't take into consideration
size of conductor, ambient temperature, length of run etc...

It may seem simplistic, but that's the answer.

Now what isn't so simple is just how hot the conductor gets when
carrying 30A vs 20A. Maybe that's what you're thinking of?

With 2.25 times the heat generated, it should take 2.25 times the
temperature difference between ambient if all other factors are the
same. So if you had a 20C rise in conductor temperature over ambient at
20A, you should expect 45C rise with 30A.

But it actually is a bit worse than that because at 30A, with a higher
temperature in the conductor, the resistance of the conductor is
somewhat higher. So the power dissipated is slightly more than 2.25
that at 20A.

If the temperature rise at 20A is more because of insulation, conduit,
embedded in a wall, etc..., than the rise for 30A will still be 2.25
times as much, but that can be too much. For example if the temperature
rise with 20A was 40C, than carrying 30A would make the rise 90C. And
that's probably too high for the equipment and insulation.

And of course if the ambient temperature is abnormally high, adding on
the same rise (either 45C in the first case or 90C in the second case),
it can still push the resulting temperature over some limits. That's
why cabling is de-rated for high ambient temperature installations.

daestrom
 
A

Andrew Gabriel

Jan 1, 1970
0
It may seem simplistic, but that's the answer.

Now what isn't so simple is just how hot the conductor gets when
carrying 30A vs 20A. Maybe that's what you're thinking of?

With 2.25 times the heat generated, it should take 2.25 times the
temperature difference between ambient if all other factors are the
same. So if you had a 20C rise in conductor temperature over ambient at
20A, you should expect 45C rise with 30A.

But it actually is a bit worse than that because at 30A, with a higher
temperature in the conductor, the resistance of the conductor is
somewhat higher. So the power dissipated is slightly more than 2.25
that at 20A.

Same effect with heating at contact and connection resistances too.
That's why really good connections are essential with high current
circuits. When heating does start, this often results in the quality
of the connection changing for the worse, and the resistance rising.
This generates more heat, and the two effects fuel each other, and
you get a runaway, resulting in the connection grossley overheating
and failing.
If the temperature rise at 20A is more because of insulation, conduit,
embedded in a wall, etc..., than the rise for 30A will still be 2.25
times as much, but that can be too much. For example if the temperature
rise with 20A was 40C, than carrying 30A would make the rise 90C. And
that's probably too high for the equipment and insulation.

And of course if the ambient temperature is abnormally high, adding on
the same rise (either 45C in the first case or 90C in the second case),
it can still push the resulting temperature over some limits. That's
why cabling is de-rated for high ambient temperature installations.

and also (in UK at least, and probably most places) derating for
cable grouping - running multiple conductors togther where mutual
heating effects result in a higher temperature rise.
 
G

Guest

Jan 1, 1970
0
The assumption is that the same conductor is used at 30A as at 20A . You
could do it, but in most jurisdictions, the codes take into account the
changes in heating and dictate appropriate wire sizes.
 
A

Archimedes' Lever

Jan 1, 1970
0
IN AN IDEAL SITUATION THAT HEAT HAS LITTLE OR NO EFFECT AT ALL
DESIGNING PARAMETERS ARE OPTIMAL AND THESE FACTORS ARE TAKEN INTO
CONSIDERATION BEFORE THE FINAL PRODUCT HITS THE MARKET OR THE CIRCUIT
COMPLETED AND DELIVERED

I AM PROETUS


You're an idiot, and google will be killing this account soon as well.

In fact, I am going to gather up ALL of the ip addresses you have google
accounts with, and forward then all to google so they can see what you
are about, and kill these accounts as well. The terms of google is that
you do not lie about your identity and you have only ONE account. They
will surely be interested in the fact that you post under several.

They will be quite interested that you are back online, abusing their
service yet again.
 
A

Archimedes' Lever

Jan 1, 1970
0
YOU ARE GOING TO HELL IN A WAVE TROLL

You are an idiot, and YOU are the troll, dipshit.
I HAVE MANY ACCESS POINTS

No, you have illegally opened multiple Google groups or google mail
accounts and they need to know about your pathetic abuse.
I CAN EVEN ROUTE THROUGH YOUR ACCOUNTS


I am sure that they will also be interested in this claim, which I
personally feel is total bullshit, because a retard like you doesn't have
the brainpower to "route through" ANY other "account", you stupid fucking
troll bastard liar.
AS YOU HAVE OFTEN DONE WITH
UNSUSPECTING USENET MEMBERS

False accusations should get you in deep shit as well, but the current
society we live in tolerates retarded fucks like you.
AND FOREGN ACCOUNTS BENIGN TO YOUR USEAGE

Nope. every post I have ever made into Usenet in the past 5 years has
been through THIS very account, you retarded piece of shit, and their
logs would also show that NO other access of ANY type has EVER taken
place from this account. Too bad that your false claims only make your
position weaker. How your retarded ass could possibly be any weaker than
it already is is surprising, but you take yourself lower with nearly
every post you make.
YOU ARE A MENACE

You are the menace. Especially when you claim to be getting access
through other people's connection. That makes you a felon.
A DANGEROUS THREAT TO PEACE AND A NUISCNACE IN THE INTERNET AT EVERY
LEVEL

Really? So, you have never listened to ANYONE when they tell you that
your all caps horseshit is abusive. You ignore everyone, and now
EVERYONE ignores you. Are you happy, dumbfuck?
YOU THINK YOUR POSITION AND AUTHORITY GRANTS YOU THE POWER TO ARASS
AND INTIMIFDATE OTHERS FROM YOUR COWARDLY HIDDEN LIFESTYLE

My authority is that of a Usenet user. Your lameness is that of a
Usenet abuser. Unless you kill the all caps horseshit, that fact will
never change.
YOU ARE NOT HIDDEN FROM GOD TROLL

You wouldn't know, since you are about as far from God as an NYC
retarded twit can get.
I WILL CONTUNUE TO PRODECUTE YOU UNTIL YOUR FIENDISH ENTERPRSIE WITH
ALL IT'S HIDDEN ASGANDAS ARE UNTTERLY DESTROYED AND VANISHED FOR EVER

I notice that you have cut out the offensive abuse. What's the matter,
asshole? Did you get some fan mail from google groups administration?
I HAVE EVEN COUGHT YOU TROLLING FOR A GAY HOMOSEXUAL RELATION ON OTHER
GROUPS

No, you haven't and you are so stupid that you wouldn't know.
TAKE A HINT END YOUR TROLLING AND LURKING AND LEAVE WHILE THE LEAVING
IS AVAILABBL;E

What? Are you going to block the gate? You're a fucking joke, boy. Or
is it Roy?
SECERAL COMPLAINTS HAVE BEEN SENT AND LOGGED ASGAINST YOU TO THE FBI
AND INTERPOL

More folks to ignore you 100%, and laugh at your pathetic ass.
I WILL ACTIVATE A HOMELAND SECURITY WATTCH


You have a hard time activating your welfare check, boy. You couldn't
activate anything more than that if you tried.
AND FIND YOU AND
DECOMMISSIOIN YOU AND YOUR FOOL HEARTY AGENDAS ALONG WITH ALL YOUR
TROLLING EQUIPMENT IF YOU PERSIST

A threat? Since it comes from a retarded little pussy punk like you, I
have no fears.
I AM PROTEUS

No, you are the retard Roy, and Google should kill every account you
have ever opened and every account you currently have, and they should
block your retarded, pathetic ass from ever opening any more ever again.
You are a pathetic little cry baby retarded twit, and nothing more.
 
A

Archimedes' Lever

Jan 1, 1970
0
On Apr 6, 9:16 pm, Archimedes' Lever <[email protected]>


YOU SHOULD NOT MAKE UP LIES

I have not lied, Roy, you fucking total retard.
NOR ISSUE THREATS TROLL

I have not threatened anyone either. Telling you that you NEED a
sledgehammer upside the head is NOT a threat, idiot. It is an opinion.
YOU ARE IN VIOLATION OF THE SAME LAWS AND RULES YOU ACCUSE OTHERS OF

I have broken no laws. You have broken laws, and you will again after
the sting from the last complaint fades from your feeble brain.
YOU ARE NOT ABOVE THE LAW

You should remember those words, idiot. They will bite YOU in the ass.
YOU WILL PAY FOR ALL YOUR OFFENSES AND BE FORCED TO MAKE AMENDS FOR
ALL THE DAMAGE YOU HAVE CAUSED WITH YOUR FALSE COMPLAIINT FILING
FROM YOUR HIDDDEN EVERS SO COWARDLY TERRORISTIC COMPUTER STATION

False complaint? Let's see which post I complained about and do a poll
as to whether or not it is abuse. These quotes are what you are about.
They show the world just how pathetic you are.


Quote from the abusive bastard Roy, who posts as "PROTEUS":

YOU ARE EITHER A REDNECK FUCKTARD OR A TROLL
A SALIVA DRIVEN DEVICE
GET A LIFE
OR AT LEAST TELL YOUR DOCTORS TO CUT BACK ON THE MIND ALTERING DRUGS

I AM PROTEUS

Yep, that one looks pretty abusive. Let's see:

THE WIZDUMB IS JUST OOOZING OUT OF YOU HERE ISN'T IT DONKEY ?

I AM PROTEUS

Yep, that one makes you look like an immature little abusive shithead
as well. Those two were one right after the other. That also says
something about just how tragic your case is. Let's try one more:


YOU ARE JUST A RELFECTION OFTHE TOTAL FAGGOTY FUCKTARD YOU WERE
NEVERTHELESS I WILL LEAVE MY DEEP ANAL PROBE IN YOUR RECTUM AS A
REMINDER JUST IN CASE YOU DECIDE TO CONTINUE HARASSING THE FINE FOLK
THAT VISIT ALTERNATE.ELECTRICAL.ENGINEERING

I AM PROTEUS

That one is about as abusive as it gets. I didn't catch that one last
time, but I can surely issue a nicely drafted complaint for that one too.
You deserve to lose everything, and you most certainly should.

How about I post it all in a nice new Google group specifically meant
to show google where their abusive posters are at? I'll bet that your
accounts would not last long after that, and I'll bet that the group
gains a HUGE popularity among folks trying to purge the net of abusive
little retarded bastards like you.
YOUR COMPANY OR ANY COMPANY THAT AIDS YOU WILL CONTINUE TO SUFFER AND
PAY AS WELL

My company is separate from my access to Usenet, you fucking total
retard.

Now take your retarded ass to a tall bridge and jump off of it, ROY!
Feeding the fishes is all your pathetic hulk would be good for.

Sad though, they wouldn't go near your stinking corpse.
I AM PROTEUS

You are Roy, and absolute total retard. The MS owned WebTV service
even TERMINATED your abusive, retarded ass. That should tell you
something, dumbfuck.
 
A

Archimedes' Lever

Jan 1, 1970
0
On Apr 6, 9:16 pm, Archimedes' Lever <[email protected]>


YOU SHOULD NOT MAKE UP LIES
NOR ISSUE THREATS TROLL
YOU ARE IN VIOLATION OF THE SAME LAWS AND RULES YOU ACCUSE OTHERS OF

YOU ARE NOT ABOVE THE LAW

YOU WILL PAY FOR ALL YOUR OFFENSES AND BE FORCED TO MAKE AMENDS FOR
ALL THE DAMAGE YOU HAVE CAUSED WITH YOUR FALSE COMPLAIINT FILING
FROM YOUR HIDDDEN EVERS SO COWARDLY TERRORISTIC COMPUTER STATION

YOUR COMPANY OR ANY COMPANY THAT AIDS YOU WILL CONTINUE TO SUFFER AND
PAY AS WELL

I AM PROTEUS


At 153rd and Morris. That is one location from which you abuse this
group.

230th and Broadway is another.

Looks like your pathetic street beggar ass gets around the slums of
Harlem.

Where else do you commit your pathetic abuse from?

Hahahahah... it figures.. it is called "Hicksville, NY"!

Bwuahahahahahhaha!

Let's see if these guys like how you post through google groups:

[email protected]

I will track you down, and I will report your abuse, BOY!
You can count on it!
 
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