Over sizing the breaker question?

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Originally Posted by performance

IF the correct plug is used, then it will be obvious, since the 6-50 is the only standard plug for single phase 220V welders and cutting equipment. The camper won't plug in.

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This may have been the case previously, but a 'standard' is not a rule, & with the emergence of multi-voltage welders/cutters this 'standard' is disappearing.
The Miller Dynasty 200DX's we have on the job are voltage sensing from 110v to 220v & as so are equipped with a neutral (4 wires out of the machine). We wire the machine with a 30amp 4 pronged plug & then run adapters for the 220v-30amp/110v-20amp outlets we may encounter when moving from area to area.

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Originally Posted by kenwhite

Like I said, every branch that has a socket has its breaker sized for the cable insulation type, cable run length, # of cables bundle togther, load duty cycle, and cable AWG size to protect the wiring. It is the manufacturers responsibility to fuse/breaker if they want to protect the end user equipment from excessive damage or fire hazards.

The breaker protects the wiring between the socket(s) and panel, it is not sized or designed to protect the equipment that is plugged into the socket.

Oh, and my furnace is hard wired into a fused disconnect and not plugged into a 120 V wall socket - this is per the manufacturers recommendation, so be careful when you use the word every...

Typically the minumum fuse/breaker size is recommended for proper operation so the circuit is not being interrupted often when trying to use the device.

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I have installed every brand of furnace sold in the US. Not one requires hard wiring and a fused disconnect per the manufacturer. If your furnace is installed that way it is because of local codes.
Very few manufacturers list a minimum fuse. Most only list a maximum fuse or breaker size.

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Originally Posted by kenwhite

The thing you have to consider when looking at the duty cycle, is that while the continuous current limit may be exceeded for short periods of time, the average current based on the duty cycle load is typically much less than rated continuous current.

If the branch has multiple loads, the breaker would still trip trip if severly overloaded when multiple loads are being used - normally a thermal breaker is specified for this type of circuit.

Article 630 is really written for commercial/light industrial use with exceptions for residential/home use of a welder.

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If a branch has multiple loads, the breaker size should equal the sum of the loads with the appropriate wire used. If the breaker is tripping as in your statement, then the wrong supply wire and breaker was installed. We install multiple appliances on a single circuit regularly for commercial buildings. We use a larger supply wire on that circuit and the larger breaker equal to the sums of the maximum of the appliances and each appliance has it's own individual fused disconnect with the appropriate size fuses for that one appliance.

There are 3 things that matter in any electrical installation, Breaker, (wire dia. size& length) and plug, The rule that must followed is: the breaker must always be the weak link. To get it right,,, you need to know your breaker size, the wire size and length of run and a proper plug or outlet for the amps.

use this calculator to checkout your setup.......... if you are near the limit of one wire size run, use a larger dia. wire for safety in your design.

http://www.gorhamschaffler.com/wire_...alculator.html

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Originally Posted by A/C Guy

I have installed every brand of furnace sold in the US. Not one requires hard wiring and a fused disconnect per the manufacturer. If your furnace is installed that way it is because of local codes.
Very few manufacturers list a minimum fuse. Most only list a maximum fuse or breaker size.

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That is funny because every HVAC forced hot air system I have seen is hardwired, and I did a quick search and found a few product manuals that require it too. In these manuals the manufacturer typically lists what type of safety disconnect and fuse/breaker is suggested too.

I have never seen a maximum fuse size listed for a plug in device, only a mimimum size for proper operation to avoid excessive tripping.

For hard wired devices, the recommended cable size, breaker/fuse, and disconnect is listed with the caveat that each installation is different and subject to local codes.

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Originally Posted by A/C Guy

If a branch has multiple loads, the breaker size should equal the sum of the loads with the appropriate wire used. If the breaker is tripping as in your statement, then the wrong supply wire and breaker was installed. We install multiple appliances on a single circuit regularly for commercial buildings. We use a larger supply wire on that circuit and the larger breaker equal to the sums of the maximum of the appliances and each appliance has it's own individual fused disconnect with the appropriate size fuses for that one appliance.

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Well, there are mimimum requirements for branch circuit design as well as load duty cycle, demand factor, requirements.

I never said the breaker would trip excessively, I said it would still protect the branch correctly even when overloaded with many circuits on the branch energized at once.

The rest of your post reinforces my previous points...

:)

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Originally Posted by DiabolicZ

I could see that happening. Just for my general pacific 50 amp breaker and 8' of #6 wire, it cost me $80.

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lucky you only had to get 8'...I had to get 75'...I sure hope it was not in waste...Starting to like I would have been ok with 8awg for a welder that draws 42 amps

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Originally Posted by geezer

There are 3 things that matter in any electrical installation, Breaker, (wire dia. size& length) and plug, The rule that must followed is: the breaker must always be the weak link. To get it right,,, you need to know your breaker size, the wire size and length of run and a proper plug or outlet for the amps.

use this calculator to checkout your setup.......... if you are near the limit of one wire size run, use a larger dia. wire for safety in your design.

http://www.gorhamschaffler.com/wire_...alculator.html

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Geezer you must derate the ampacity of a cable if the wires are bundled togethter.

Also, insulation type determines how much current a particular sized cable can carry. For example, 3 wires bundled together operating at 30*C (86*F) have the following ratings:

6 AWG THHN -> 75A rating when at 30*C and can be operated all the way up to 90*C (194*F) with proper derating.

6 AWG THHW -> 65A rating when at 30*C and can be operated all the way up to 75*C (167*F) with proper derating.

6 AWG UF -> 55A rating when at 30*C and can be operated all the way up to 60*C (140*F) with proper derating.

If there are more wires in the bundle than 3, the ampacity goes down. If the ambient around the wires is higher than 30*C, the ampacity goes down.

So there is really more to correct power distribution design than just wire size and length...

There seems to be some confusion on demand factor and duty cycle, so I though I would try to clarify both.

Demand factor is based on the premise that the actual load at any given instance in time will always be less than the sum of the total loads used within any given installation.

If we add up all of the loads and size our electrical design for them -> microwave, TV, Stereo, garbage disposal, stove, furnace/air conditioning, etc, etc..., we would have very large, expensive, cable runs to handle a current draw that would not exist.

So, the NEC allows for the total load to be reduced by a number called a "demand factor" when sizing branches - the breaker will still protect the wiring should the load for a given cable be exceeded under an unsual circumstance.

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Now for the duty cycle explanation.

Power is the rate of energy consumption per unit time -> Joules/Second.

Joules are a form of heat, and internal heating is what damages the cable's insulation.

In order to determine internal heating for a cable, I^2*R, the current must be measured in what is called Root/Mean/Square values - this value produces the same heating as an equivalent DC source.

EXAMPLE: A current pulse of 100A that is turned on for 2 seconds and turned off for 8 seconds produces an RMS (heating value) calculated by:

(100A)^2*2 seconds + (0A)^2*8 seconds -> Squared area = 20,000 A^2*S

(20,000 A^2*S)/10 S -> Mean = 2000 A^2

(2,000 A^2)^0.5 -> Root = 44.72 Amps

So, you can see the 100 amp pulse described above only produces heating that is equivalent to a 44.72 Amp continuous current source, so why design for a 100 Amp circuit?


The bottom line is that wiring is not a simple plug and play game, it requires some thought and experience.

If you can't read and use the NEC effectively, then you should probably hire a qualified electrician to either help or perform the installation.

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Originally Posted by kenwhite

Geezer you must derate the ampacity of a cable if the wires are bundled togethter.

Also, insulation type determines how much current a particular sized cable can carry. For example, 3 wires bundled together operating at 30*C (86*F) have the following ratings:

6 AWG THHN -> 75A rating when at 30*C and can be operated all the way up to 90*C (194*F) with proper derating.

6 AWG THHW -> 65A rating when at 30*C and can be operated all the way up to 75*C (167*F) with proper derating.

6 AWG UF -> 55A rating when at 30*C and can be operated all the way up to 60*C (140*F) with proper derating.

If there are more wires in the bundle than 3, the ampacity goes down. If the ambient around the wires is higher than 30*C, the ampacity goes down.

So there is really more to correct power distribution design than just wire size and length...

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Interestings facts to be sure if the welder is being installed in a submarine or some other critical area with all the cables bundled, However my purpose is to simplify it for a fellow trying to make a single run from his panel box to the end of his shop/garage. Throwing in fractional calculations although accurate do not do any thing except add to his confussion. Rather than argue amongst ourselves about who is exactly right, let us step back and solve the problem for him in a form he may understand.

The simplist answer I can give anybody is: when in doubt use a big thick wire

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Originally Posted by geezer

Interestings facts to be sure if the welder is being installed in a submarine or some other critical area with all the cables bundled, However my purpose is to simplify it for a fellow trying to make a single run from his panel box to the end of his shop/garage. Throwing in fractional calculations although accurate do not do any thing except add to his confussion. Rather than argue amongst ourselves about who is exactly right, let us step back and solve the problem for him in a form he may understand.

The simplist answer I can give anybody is: when in doubt use a big thick wire

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Well, the ampacity for a single cable installation is derated too, but that rarely occurs since everything needs at least a hot and return and a safety ground.

While your advice may be sound in some instances, there is a lot more to electrical work than that.

The OP discussion is about why it is "not recommended to over size a breaker" and there were many reasons/theorys discussed when it is appropriate to over size and when it is not.

So while the technical discussion may be boring, it is required if you want to upgrade according to code which is based on safe, sound, operating principles that can be implemented in a some what easy and cost effective way.

:)

The solution to this debate is actually a simple one..
Apply for the proper 'permit', which is usually a requirement when adding to or upgrading an existing electrical panel/service, & the inspector will let you know whats 'required/acceptable' in your locale.

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Originally Posted by ASE_MasterTech

The solution to this debate is actually a simple one..
Apply for the proper 'permit', which is usually a requirement when adding to or upgrading an existing electrical panel/service, & the inspector will let you know whats 'required/acceptable' in your locale.

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You realize you just took all of the fun out of this thread, LOL

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Originally Posted by ASE_MasterTech

The solution to this debate is actually a simple one..
Apply for the proper 'permit', which is usually a requirement when adding to or upgrading an existing electrical panel/service, & the inspector will let you know whats 'required/acceptable' in your locale.

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Or Call a licensed and insured electrical contractor and sleep well at night.:D

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Originally Posted by Ram48

Or Call a licensed and insured electrical contractor and sleep well at night.:D

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Yep, and I think I said that once or twice...

:)

I can think of only one anwser to this post:

"There is never time to do it right but there is always time to do it over!"

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Originally Posted by Canada

I can think of only one anwser to this post:

"There is never time to do it right but there is always time to do it over!"

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There's not always time to 'do it over', particularly when your house/shop is a pile of ash.
just a thought...

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There's not always time to 'do it over', particularly when your house/shop is a pile of ash.
just a thought...

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That was the point. How many times have you heard someone say they don't have time to do it right. After it fails they always find time to do it over. In other words do it right the first time, every time.