Sam or Mary Yancy on fri 9 jan 04
I understand needing the proper circuit breaker for the kiln specified, but I don't understand why you could not wire the kiln with the largest guage wire as you can afford or you want - reason - for possible upgrade of a kiln to a larger one later - by just upgrading the circuit breaker. Comments please. Sam in Daly City
piedpotterhamelin@COMCAST.NET wrote:
If your electrical power supply is 240 volts, your large kiln is computed at 50 amps and requires a 60 amp breaker and a larger gauge wire. Your smaller kiln is rated at 23 amps and requires a 30 amp breaker with a smaller gauge wire .......
Bruce Girrell on sat 10 jan 04
> I understand needing the proper circuit breaker for the kiln specified,
>but I don't understand why you could not wire the kiln with the largest
>guage wire as you can afford or you want
The way that you understand it is correct. Unless the laws are vastly
different in the UK, the only restriction on conductor size for this
application is a minimum conductor size. To be completely honest, I could
not find pottery kilns addressed in the National Electrical Code. The most
applicable article that I could find was Fixed Electric Space-Heating
Equipment, which covers electric furnaces. The only applicable comment there
regarding conductor size is:
The ampacity of the branch circuit conductors and the rating or setting of
overcurrent protective devices supplying fixed electric space-heating
equipment consisting of resistance elements with or without a motor shall
not be less than 125 percent of the total load of the motors and heaters.
I also checked out welders, general wiring practices, and branch circuits.
Nowhere was there mention of a _maximum_ conductor size.
Ask your electrician for the wording of the building code or electrical code
that requires the smaller wiring. I'd be interested to see it.
Bruce Girrell
in cold, snowy northern Michigan
where today we have a massive line blend going on - emulating Tichane's work
on celedons but for our own clay body.
martin on sat 10 jan 04
But is it art...?
On Jan 10, 2004, at 11:54 AM, piedpotterhamelin@COMCAST.NET wrote:
> Wiring is not at times as simple as it appears!
> The type of wire or insulation, gauge, voltage drop. So many things.
piedpotterhamelin@COMCAST.NET on sat 10 jan 04
Hi.
> I understand needing the proper circuit breaker for the kiln specified,
> >but I don't understand why you could not wire the kiln with the largest
> >guage wire as you can afford or you want
I simply stated that the connectors might not take the increase wire diameter.
Increasing the wiring gauge can offset voltage drop in the current. Voltage drop is determined by Ohm's law; voltage drop = amperes X ohms. A voltage drop of no greater than 2 percent is recommended; a drop above 5 1/2 percent not tolerated.
The example in my book states the following: If a 500 watt light is installed 500 ft from a branch circuit breaker it would require a total of 1000 ft. At 120v the 500 watt lamp draws 4.2amps. If number 14 is used, resistance is 2.57 ohms per 1000 ft, voltage drop is 10.8 volts, far over 2 percent, It is 9 percent. No 6 would give a drop of 1 1/2 percent at 1.7 volts.
Other things to consider:
insulation withstands
least heat best
TYPES T AND TW TYPE THW
Wire size Diam. resist ohm/100feet Max current/voltage drop per 100feet
10 .102 .098 30A/2.9V 30A/2.9V
8 .128 .062 40A/2.5V 45A/2.8V
6 .184 .039 55A/2.1V 65A/2.5V
4 .232 .024 70A/1.7V 85A/2.0V
"Cautions about Ampacity- You must always use a size and type of wire that has an ampacity rating at least as great as the number of amperes to be carried. For short runs, voltage drop tables may show a wire size smaller than is permitted for the current involved. Use wire with sufficient ampacity. Voltage drop for any given current, at any distance, depends solely on the circular-mil area of the wire: ampacity of any size and kind of wire varies withthe kind of insulation and other factors. Using wire that has a higher ampacity in any given size, than another type of wire of the same size will not reduce voltage drop." "If a wire has a temperature rating of say, 60'C or 140'F (which is the lowest temperature rating assigned to any kind of wire) it does not mean that the wire may be used where the ambient temperature is 140'F. It means that the temperature of the wire itself may not exceed 140'F. It will reach that temperature when carrying its rated current in a room where the ambient temperature is 30'C or 86'F. If the room ambient temperature is higher than 86F and the wire is carrying its full rated current, its actual temperatuer will exceed its temperature rating of 140F. Th
erefore, if any kind of wire is installed in hot locations, its ampacity is reduced from that shown in the tables NEC 310-16 to 310-19. Wire installed installed in free air has a higher ampacity than wire in conduit or buried, which cannot radiate the heat." "The ampacity of a wire, while not directly in proportion to its surface area, is more related to its surface area than to its cross-sectional area. No. 12 wire as compared to a No. 6 wire will have twice the diameter, circumferance and surface area but four times the cross-directional area of the smaller wire. A wire that has four times the cross-directional area of another has only twice the surface area of the smaller wire and the heat developed in the wire can be dissipated from its surface." This surface area is what determines the amperage rating of 20 for No. 12 and 65 for number 6.
Wiring is not at times as simple as it appears!
The type of wire or insulation, gauge, voltage drop. So many things.
Rick
--
"Many a wiser men than I hath
gone to pot." 1649
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