If it were that simple, so would be the codes. You asked a lot of questions without reducing the scope. Answers depend on the application. For example ampacity depends on temperature which in turn depends on environment (ambient, buried, aerial, in conduit, in concrete, or other dissipation factors, insulation thickness, accompanying conductors which can contribute heat, insulation temperature rating, conductivity (aluminum, copper), length, time, etc). For wiring typical of product interiors, product standards such as IEC 60950 will provide a simpler set of answers, but for building installations, the best approach is to get a copy of the code (for ease of use, I'd recommend the NEC handbook which includes the code) and look up the rules for the materials and wiring methods used. See some specific notes added below.
Bob Johnson Peter Merguerian wrote: > Dear All, > > Does anyone have a resource for a "Rule of Thumb" method for the > following pertaining to permanently wired equipment in the US and > Canada? I am looking for something that is "to the point" and > without having to use the NEC/CEC. > > 1. Determine the ampacity of conductors anticipated in the field. NEC tables 310-15 thru -21, -61 thru -81, 400-5 and 402-3 all cover ampacity of conductors under varying circumstances. You can try #12 AWG for most 20 amp branch circuits, but it depends. > 2. Determining the overcurrent protection devices ahead of the > equipment. There are over fifty articles for general branch circuits and specific conditions such as communications equipment and countinuous loads like ITE equipment. Our typical 15 and 20 amp receptacles are protected by 20 amp and sometimes 15 amp devices, and can be loaded to 80% of the receptacle rating (12 and 16 amps respectively) for continuous loads. Circuit breakers are most common but you may find fuses. Circuit breaker curves have changed recently. > 3. Determining Wire Bending Space. Bending radius must be at least 8 times the overall diameter, 12 times for shielded conductors, 12 times the diameter of individual conductors in a multiconductor cable and 7 times the overall diameter, although it also depends on the wiring system. See article 300-34 > 4. Determining the Volume of the Wiring Compartment. Depends on the use. For outlet, device and junction boxes and conduit bodies, the volume depends on conductor size, 2.25 cu.in. for 12 AWG. The permitted fill is specified for each of the small box sizes, and calculated for larger boxes. Fill includes count of clamps, support fittings, yokes, and devices. For example a typical outlet box with 12-2/G wires feeding thru would count 4 conductors (phase & neutral, in & out), 1 ground (all grounds count as one - usually), clamp and receptacle, for a count of 7, requiring a 3x2x3.5 device box. See article 370-16. > 5. Determining the size of the Conduit Opening or the Knockout > Opening. These can be found in UL 1950 Table NAE.2. A few sizes are 1/2 in trade size, 7/8 in dia; 3/4 trade, 1-3/32 dia; 1 trade, 1-23/64 dia. > > 6. Determining the Size of the Earth Bonding Conductors? Here we have a good rule of thumb. Make it the same size as the phase conductor unless you're above 30 amps. Then you can look up smaller sizes in clause 250-122. > > PETER S. MERGUERIAN > MANAGING DIRECTOR > PRODUCT TESTING DIVISION > I.T.L. (PRODUCT TESTING) LTD. > HACHAROSHET 26, P.O.B. 211 > OR YEHUDA 60251, ISRAEL > > TEL: 972-3-5339022 > FAX: 972-3-5339019 > E-MAIL: [email protected] > Visit our Website: http://www.itl.co.il > > --------- > This message is coming from the emc-pstc discussion list. > To cancel your subscription, send mail to [email protected] > with the single line: "unsubscribe emc-pstc" (without the > quotes). For help, send mail to [email protected], > [email protected], [email protected], or > [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
