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Wattage of Refrigerator: Safe to Use This?


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2 hours ago, bankruatsteve said:

Is that for 100m of cable?  Wouldn't it be different for 1m?

 

It makes no difference.

 

The current rating of the cable doesn't change with length. The resistance and thus the volt drop increases with the run length so the voltage at the far end can drop to unacceptable levels but the cable isn't going to be damaged.

 

An example.

0.75mm2 copper has a resistance of about 2.6 ohms per 100m, so a 100m run (out and back) will have a resistance of 5.2 ohms.

At its rated 6A that will drop V=IR = 6 * 5.2 = 31V  about 15% @ 220V. Enough to upset some appliances.

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Worry seems to be about the extension but what about the power point itself and what all is connected to that circuit? Old house or apartment this plug may be part of just one circuit that is already

fridge 160 Watt max. theoretically, 'yes' never did trust those extension leads though....

And that the Bangkok Cable website rates that at 6A in free air  http://www.bangkokcable.com/product/backoffice/file_upload/131004_20-300!500V 70C 60227 IEC 53-3C (GNYE).pdf   Pretty we

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So there you have it.

 

My verdict: I'll try to change the extension if I can to a thicker cable (I dunno how easy it is to do that in Thailand).

 

If they don't let me, I'll just use it as is, since it's rated for it by "Thai industry standards" and just not leave it unattended.

 

Longest I ever use the oven is 30 minutes straight, and never at the maximum temperature of 230 C, probably 220 C at *most*.  (My normal practice for all appliances even my cooking stove is to never use the highest setting) 

 

 

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10 minutes ago, Crossy said:

 

It makes no difference.

 

The current rating of the cable doesn't change with length. The resistance and thus the volt drop increases with the run length so the voltage at the far end can drop to unacceptable levels but the cable isn't going to be damaged.

 

An example.

0.75mm2 copper has a resistance of about 2.6 ohms per 100m, so a 100m run (out and back) will have a resistance of 5.2 ohms.

At its rated 6A that will drop V=IR = 6 * 5.2 = 31V  about 15% @ 220V. Enough to upset some appliances.

Well, then it does make a difference.  Resistance is what will heat the cable not the voltage.  🙂

 

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8 minutes ago, bankruatsteve said:

Well, then it does make a difference.  Resistance is what will heat the cable not the voltage.  🙂

 

1m of our cable (0.026 ohms) with 6A flowing will dissipate I2R = 36*.026 = 0.936 Watts.

 

It doesn't matter if that 1m is on its own or part of a 100m run. The 100m will dissipate 93.6 Watts in total, but each metre will still be dissipating 0.936 Watts.

 

 

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21 minutes ago, junkofdavid2 said:

My verdict: I'll try to change the extension if I can to a thicker cable (I dunno how easy it is to do that in Thailand).

 

Look for a lead with a cable marked as "3 x 1.0mm2" which would be a "real" 10A rated cable. Sadly, I'm not sure you'll score.

 

As noted earlier, it will likely be fine, it's only a 15% overload, it will certainly get warm but shouldn't be a significant hazard. 

 

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44 minutes ago, Crossy said:

 

1m of our cable (0.026 ohms) with 6A flowing will dissipate I2R = 36*.026 = 0.936 Watts.

 

It doesn't matter if that 1m is on its own or part of a 100m run. The 100m will dissipate 93.6 Watts in total, but each metre will still be dissipating 0.936 Watts.

 

 

Maybe i am just arguing with dead brain cells and for that I will apologize.  And I can't seem to Google an answer.  But what I recall is that electrical energy to heat energy is a relationship of amps, resistance and time.  To me the resistance would be the total resistance versus an incremental part of the load.  I'm thinking 100m of cable will get hotter over time than 1 m of the same cable.  And I'm sure, in the states anyway, both wire size AND length affected the amp rating of extension cords.

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8 minutes ago, bankruatsteve said:

I'm thinking 100m of cable will get hotter over time than 1 m of the same cable.

 

It will certainly dissipate 100x more power, but that power will be spread over 100 times the length. This is one reason why one shouldn't use your extension whilst coiled, the heat can't get out and things melt (or worse).

 

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8 minutes ago, bankruatsteve said:

I'm thinking 100m of cable will get hotter over time than 1 m of the same cable.

It also depends on how the 100m of cable is laid out as my mother found out when running about a 1kW or 2kW load without uncoiling the much shorter (maybe about 10m) extension and smelling the unmistakable odour of melting PVC. She lucky found it before it actually caught fire, but not much before. The extension became about a ½m one 😉 

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5 minutes ago, Crossy said:

 

It will certainly dissipate 100x more power, but that power will be spread over 100 times the length. This is one reason why one shouldn't use your extension whilst coiled, the heat can't get out and things melt (or worse).

 

I think that it’s not only heat from the load but also from the interaction of the magnet field, isn’t it!

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27 minutes ago, bankruatsteve said:

And I'm sure, in the states anyway, both wire size AND length affected the amp rating of extension cords.

An example from Lowes.  And with that, I quit.  😉

ext cord.jpg

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Well, just one more.  I Googled:  "Hence the heating effect produced by an electric current, I through a conductor of resistance, R for a time, t is given by H = I2Rt."

 

Which would be an exponential effect of I not just linear effect of R.

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1 hour ago, bankruatsteve said:

Which would be an exponential effect of I not just linear effect of R.

 

Yup. But for our purposes I is a constant.

 

Why not do some worked examples?

 

The actual current rating of the cable does not change with length. Other important factors (volt drop) do change.

 

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1 hour ago, bankruatsteve said:

An example from Lowes.  And with that, I quit.  😉

ext cord.jpg

 

12 AWG cable is typically rated for 20A or so, right hand unit. (not sure what the connectors are if any)

 

The left hand unit has US 15A connectors which is what is limiting the rating rather than the cable.

 

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21 minutes ago, Crossy said:

 

Yup. But for our purposes I is a constant.

 

Why not do some worked examples?

 

OK. Then using above, 100m of cable would generate 600 times more heat than 1m. ?? I have no idea how cable is rated but suspect it's very conservative and recall (caveat dead brain cells) that short lengths of cable have more capacity due to the issue of overheating. 

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12 minutes ago, bankruatsteve said:

OK. Then using above, 100m of cable would generate 600 times more heat than 1m. ?? I have no idea how cable is rated but suspect it's very conservative and recall (caveat dead brain cells) that short lengths of cable have more capacity due to the issue of overheating. 

 

No, 100m will generate 100 times more heat in total assuming the same current through each (which negates the square law).

 

OK, if you recall that. Better if you can provide a source.

 

Cable is rated in Amps (and Volts for insulation), it is pretty conservative but the rating is for a conductor temperature of 75C.

 

See my signature.

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