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*To*: tesla-at-pupman-dot-com*Subject*: Re: I Need Electrical Help!*From*: "Tesla list" <tesla-at-pupman-dot-com>*Date*: Sun, 11 Feb 2001 12:28:37 -0700*Resent-Date*: Sun, 11 Feb 2001 12:42:47 -0700*Resent-From*: tesla-at-pupman-dot-com*Resent-Message-ID*: <ENiC7C.A.AiD.0suh6-at-poodle>*Resent-Sender*: tesla-request-at-pupman-dot-com

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jimlux-at-earthlink-dot-net> This can potentially work, but has a number of pitfalls (aside from the "non-code" part you already identified). 1) The current won't necessarily divide evenly. It depends on the series resistance between the distribution panel and the join point on each leg, and also on how much load is on each leg already. Example: Typical max resistance in one branch is around a tenth of an ohm.(to meet the code requirement of max 2% drop at rated load) Say one leg is 0.05 ohms and one is 0.1 ohms. Simple Ohm's law calcs will show that one leg will carry twice the current of the other (that is, the current will divide 66/33 instead of 50/50). Now add in the uncertainty of the resistance at the plug/receptacle joint, your extension cords, etc. If your receptacles are fed from subpanels, fed by bigger feeders (very common in non-residential situations), then this applies in spades, with the additional hassle that the voltage at the subpanel may vary depending on how much load there is on the whole subpanel, which will then cause your currents to distribute unevenly. In fact, if your load isn't connected, you might even be feeding power from one circuit to the other. Example: Same as above, branch circuit resistances are 0.05 and 0.1 ohms (call them circuit A and B, respectively). A 10 Ohm load (around 10-12 Amps) connected on each branch (not your load, something else already there...). We'll make the numbers easy by assuming 100VAC. The voltage on Load A is going to be 99.5 volts. The voltage on Load B is going to be about 99 volts (i.e. more drop in the branch circuit). Now, connect your lashup between circuit A and B, with no load. Assume it has a resistance of , say, 0.01 ohms on each leg, so you've effectively connected 0.02 ohms between Load A and Load B. A little calculation will show that the voltage on B will rise a bit, and that on A will fall a bit, because some current will now be flowing from A to B, through your cords. 2) The big safety reason. When you do this, you are "backfeeding" one of the circuits, so that if it is turned off (say, by the circuit breaker tripping), the entire load will now be supplied by the remaining circuit, feeding through your lashup. Bad news indeed, especially when you think that because of the uneven distribution that is inevitable, one circuit's breaker will probably trip before the other. The saving grace is that if the first breaker tripped, the second one is likely to trip right away, since it probably is overloaded by a factor of 2. A better way (but not great) to get more power from two outlets is to find two outlets that are on opposite phases (i.e. there is 240V between them). Run through a dual ganged breaker to your load. This still has the problem that if only one branch circuit feeder trips, you are going to backfeed, but at least it is through your load. ----- Original Message ----- From: "Tesla list" <tesla-at-pupman-dot-com> To: <tesla-at-pupman-dot-com> Sent: Sunday, February 11, 2001 10:04 AM Subject: I Need Electrical Help! > Original poster: "Drew Murray by way of Terry Fritz <twftesla-at-uswest-dot-net>" <drewallmighty-at-hotmail-dot-com> > My plan was to take two extension cords and clip off the female connectors. > i will then use a multimeter to test and see if the neutrals and the grounds > are on the right wires. Sometimes i have noticed that the hot and the ground > are mixed up on non professionally installed wall plugs. I plan on taking > the hots and the grounds on the cords and connecting them together and > attaching a length of 30a rated wire to them and using marettes to hold them > together. This i think will allow 15a to flow through each cord and 30a > through the bigger cord to my 120-240v step up transformer and then to my > pt. I will be sort of sharing two 15 amp breakers to get 30 amps. > Is this possible or will i burn the school down? It may not be code but will > it work? Somebody let me know before i go ahead and try it anyway!

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