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Old 03-05-2019, 04:20 AM   #31
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Re: 20 receptacle On 30 amp breaker


While chandler48 wrote
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Originally Posted by chandler48 View Post
You cannot connect a single 20 amp receptacle to a 30 amp breaker. In essence you are overprotecting the circuit and the receptacle can melt.
How is a 30 A breaker protecting a 10-2 cable "overprotecting" the circuit?
Considering that a NEMA 5-20 (20 A) socket outlet is designed to allow a NEMA 5-15 (15 A) plug to be inserted into it so that the circuit protection level is 33% greater than the design level of the plug, how likely is it that lower capacity devices would "melt" before a protection device rated at 50% higher than design of the plug/socket combination did its job?

dmxtothemax quoted
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Originally Posted by detroit48210 View Post
Ok it is not allowed but i would like to know if this is a safety hazard and dangerous if it is not allowed but works fine and nothing is wrong that that is okay with me and i will change the receptacle if told otherwise
and responded with
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Originally Posted by dmxtothemax View Post
Yes it is a safety hazard,
You have a 30A breaker a 30A cable but only a 20A outlet.
Therefore the outlet is NOT protected from over current.
Seperate the outlets,

Put two single 20A outlets side by side,
One for the dryer and one for the washer.
These could run off the 30A line.
Now, why would two 20 A outlets make any difference, since it would be quite possible to use only one of these?

However, it is NOT the outlet that needs to be protected by any circuit breaker but it is the building wiring.

jbfan responded to dmxtothemax writing
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Maybe down under this si allowed, but not in the NEC, General use receptacles can not be installed on a breaker larger than 20 amp.
While I have no wish to bring into question any NEC regulations, it is quite true that in Australia/New Zealand the "normal" 230V 10 A socket outlets are installed on circuits protected by 20 A breakers - as are 15 A outlets. (See AS/NZS 3112)
(When protection was provided by fuses [which is no longer permitted], these fuses were rated at 15 A.)

In the UK, 13 A socket outlets are connected on "rings" protected by 32 A breakers or on "spurs" protected by 20 A breakers, (See BS 1363)
Of course, the plugs inserted into those UK socket outlets have integral fuses rated at 13 A or lower.

These Australian/New Zealand/UK 20 A (32 A ring) circuits use copper wiring with 2.5 Square Millimetre Cross Sectional Area (CSA) - which is just slightly smaller than 13 AWG.
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Old 03-05-2019, 07:37 AM   #32
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Re: 20 receptacle On 30 amp breaker


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Originally Posted by FrodoOne View Post



How is a 30 A breaker protecting a 10-2 cable "overprotecting" the circuit?


Over current protection must be sized to the smallest ampacity of any element of the branch circuit. You deliberately omitted the receptacle which in this case is 20A this that is the max breaker for this branch.

This is basic stuff. Not sure why the heavy debate here. It’s not in the gray area or ambiguous in any way.



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Old 03-05-2019, 07:43 AM   #33
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Re: 20 receptacle On 30 amp breaker


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Originally Posted by jbfan View Post
Maybe down under this si allowed, but not in the NEC, General use receptacles can not be installed on a breaker larger than 20 amp.


You are correct 15A and 20A receptacle can be protected wit 20A breaker but not with 30A, it will melt. if there is 30A circuits everything on it must be rated 30A
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Old 03-05-2019, 10:16 AM   #34
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Re: 20 receptacle On 30 amp breaker


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Originally Posted by Malywr View Post
You are correct 15A and 20A receptacle can be protected wit 20A breaker but not with 30A, it will melt. if there is 30A circuits everything on it must be rated 30A
While it may not be allowed to install a 15 A or 20 A socket outlet on a circuit protected by a 30 A breaker, the socket outlet will not melt under normal operating conditions.
Also, a 20 A socket outlet will not melt if it is overloaded by 50% with 30 A.
If it is overloaded by 200% with 60 A it will still not melt but the circuit breaker should operate within a short time and protect the wiring of the building because that is what the breaker is designed to do.

If a device which contains a short-circuit fault is plugged into any socket outlet, a very high current will be drawn and the circuit breaker will operate within a short time.
The plug pins and the socket outlet contacts will probably suffer arcing damage which may require that the socket outlet be replaced but the outlet itself will not melt.
(The heating by the extreme overload current may cause the socket outlet female contacts to loose tension rendering the socket outlet unsuitable for further use.)

To have any part of a plastic outlet "melt" requires that there be poor contact between the female socket connections and the plug pins with a current that is relatively high but less than that which will cause the circuit breaker to operate within a short time (say between about 20% and 150% of the rated current.)

This heating due to poor contact may cause the female contacts to loose tension against the pin(s) of the plug causing even less contact (increased resistance) and greater heating. In other words, a "runaway effect".


By the way, every time you unplug a high current device (such as an Iron, Toaster, Vacuum Cleaner etc.) after use I suggest you feel if the pins on the plug are appreciably "warm". If so, this would indicate that the socket outlet which you have been using is making weak contact and may need replacing.

If a rewirable plug is involved and the plug away from the pins is warm it may indicate a loose connection within the plug.
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Old 03-05-2019, 10:24 AM   #35
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Re: 20 receptacle On 30 amp breaker


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Originally Posted by curiousB View Post
Over current protection must be sized to the smallest ampacity of any element of the branch circuit. You deliberately omitted the receptacle which in this case is 20A this that is the max breaker for this branch.

This is basic stuff. Not sure why the heavy debate here. It’s not in the gray area or ambiguous in any way.
I was not "debating" the issue.

I wrote
"While I have no wish to bring into question any NEC regulations, it is quite true that in Australia/New Zealand the "normal" 230V 10 A socket outlets are installed on circuits protected by 20 A breakers - as are 15 A outlets. (See AS/NZS 3112)
(When protection was provided by fuses [which is no longer permitted], these fuses were rated at 15 A.)"
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Old 03-05-2019, 11:21 AM   #36
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Re: 20 receptacle On 30 amp breaker


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Originally Posted by FrodoOne View Post
I was not "debating" the issue.


Oh really. A obvious and simple application of regulation yet you want to suggest when plastic will melt and flow and advise deviating from code is “probably ok”.

You are also incorrect state the breaker is to protect the wires. Wrong. It is to protect the branch circuit, wires, switches, receptacles, disconnects,...

No online novel or self rationalization will change this.

Let it go.







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Old 03-05-2019, 09:59 PM   #37
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Re: 20 receptacle On 30 amp breaker


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Originally Posted by curiousB View Post
Oh really. A obvious and simple application of regulation yet you want to suggest when plastic will melt and flow and advise deviating from code is “probably ok”.
I was not suggesting that deviating from code is “probably ok”.

I was merely pointing out that there is a large "margin of safety" built in to everyday electrical equipment!
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Old 03-10-2019, 12:00 PM   #38
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Re: 20 receptacle On 30 amp breaker


Margins of safety.
Experience has proven that over time, taking chances will eventually catch up to you.
The safest thing to do is follow the absolute guidelines.
Besides the possibility of arcing, or heating wearing on the device and eventually possibly causing failure.
Your life is more important than a few dollars of cost.
And also, why take the chance of the insurance company denying your claim because you didn't follow the rules/code?
Whatever the reasoning is behind, it makes sense to do something, or it's unlikely something bad will ever happen. You should protect yourself against loss whenever possible.
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