Bear with me on this one… Our 20-circuit 100-amp board is straining and now we’re considering adding CAC. Issue is not ampage, we have a relatively small house, the issue is circuits. Electrician doesn’t think we’ll pass inspection piggy-backing all the circuits we need. So we start talking about 30-circuit board, and then we’re talking 40-circuit 200-amp service.
I’ll spend my own time thinking about scenarios where we might need more than 30 circuits (does lack of grounding due to BX have any bearing? requires more GFCI?).
But here’s a nagging thought: My office has the service entry on the other side of the wall. When I’m stretched out in my chair my toes tingle, and my computer monitor flickers sometimes. Nothing to do about it short of putting in a Faraday cage I suppose, I hear they’re about $10M room-sized. I have a co-worker who lived in an office with sigificant EMR from street power lines who has MS. Of course that has nothing to do with it…. But would 200 amps service increase the level of EMR I would be exposed to?
Replies
The amount of magnetic radiation depends on the amount of current that is flowing at any one time. That cahnges with the amount of the load, not the size of the service. If you are that concerned about it then forgo the AC.
Electric fields are determined by the supply voltage, again that is not changed by increasing the service amperage.
But if 100 amp service is all you need why not get a 40 slot pannel and install a 100 amp main?
200 amps vs 100 is just the amount of current it takes to trip your main breaker. If you only have 22 amps worth of stuff running, the electromagnetic effects will be identical no matter which panel you have feeding it.
Flickering of your monitor is unlikely to be due to EMR, it's more likely an intermittent resistive connection somewhere. Does it correspond to some other electrical event, maybe the fridge kicking on?
Tingling toes are very unlikely to be related to your electrical service. More likely to be a circulatory or nerve thing. With 120/240 volt systems, you pretty much have to touch two different pieces of metal or other conductive things to get a tingle. That's why your electric service has a ground rod, to keep the metal enclosures of the system and the ground or damp concrete you might be standing on at the same potential.
Capacitance will sometimes put 30 - 80 VAC or so on a floating piece of conduit, but at an extremely high impedance. I've gotten jingled by that at times.
So, replace the panel. Then turn off the juice and go through the whole system some bright early weekend day, open up every box, and make sure that all the devices are in good condition, all the wire nuts are on tight, everything's clean and grounded, etc. Sort of a complete electrical tune-up for the house. Then if your toes still tingle, it's the doctor you need, not the electrician. ;-)
-- J.S.
If your toes tingle and your monitor flickers, it's not because you have a breaker panel nearby. It may be because of that ungrounded BX or some other wiring problem, but that's independent of the size of the service.
In any event, what little EMR does radiate freom the panel and associated wiring is dependent only on the voltage (which is constant) and the ACTUAL current flowing. If you have a 200 amp service but only use 60 amps you only get 60 amps worth of EMR.
Re a Faraday cage, you can build your own with copper screen. I don't know what copper screen runs these days, but I'd think a few hundred would do it.
EM from a panel is very small. First the voltages and currents are low. Unless you have everything running at once I suspect you might be pulling 30A at any one time outside resistance heating, AC or a major electric appliance running.
Second EM fields operate on an inverse square formula. Whatever you read at one inch away is four times what you would get at two inches. At eight inches you are getting 1/64th of the original field strength. By the time you get to the distance between the panel and your seat on the other side of the wall any EM field is very weak.
The other consideration is that EM fields are blocked by the grounded steel case of the panel. The cabling, depending on the system, are a different story but their emissions are still subject to the same factors mentioned above. Low strength fields at a distance are less a problem.
If your that sensitive you could look at more likely sites of long term exposure. Where you sleep is a prime spot. Remember 1/3 of your time, roughly is in this one spot. Water bed heaters and electric blankets are much larger and closer sources of EM. A clock radio a few inches from your head is also a possible source. Even here the evidence of any actual harm is shaky at best. Even the best studies I have seen are all over the place. If there is any real and consistent effect it has to be subtle.
As far as the number of circuits go there is a good chance that 20 circuits are more than enough. The electrician can look at what is on each circuit and the likely load. A careful analysis will likely show that some of the circuits can be combined without causing problems. This is much easier and cheaper than installing a new panel or playing with tandem breakers.
Edited for spelling
Edited 4/30/2004 5:24 pm ET by 4Lorn1
Thanks all for your very informative answers to my fairly uninformed question.
Edit: To the question of why not just put in 40-circuit box: Well for example the Square D QO panel (recommended here recently) requires 125A to get 20 circuits and 200A to get 40 circuits.
Actually I see that they now have a 32-circuit 100A box, probably for just our kind of situation.
Edited 4/30/2004 2:10 am ET by Taylor
"To the question of why not just put in 40-circuit box: Well for example the Square D QO panel (recommended here recently) requires 125A to get 20 circuits and 200A to get 40 circuits."
They don't REQUIRE that much amperage. That is the highest that the pannel is rated for. You can always use a smaller main breaker.
Minor thread hijack: I looked at a set of house plans recently and they had some interesting requirements for the electrical. To minimize supposed negative health effects from EMR, plans stated that the electrician would be obliged to put a load on every circuit in the house and measure the field created. There was a specified threshold that was not to be exceeded. My thought was, I have no idea how that measurement would be made (and I suspect that the electricians I deal with would toss those plans out as soon as they saw that requirement). Can one of you shed some light on this? Also, isn't there also EMR from the appliances and whatnot we use in the house?
If wiring is done properly such that hot and neutral always reside in the same jacket (with current balanced) then the EMR from a cable is really quite small more than about 10 inches from it. You can reduce this even further with metal conduit.
Likewise, something like an oven, with the heating coil contained entirely within a metal envelope, has very low radiation.
The classical high radiation appliance is a heating blanket, since the input and output wires may go into the blanket at opposite ends (though more recent designs maintain "balance" even within the blanket).
But that's not to say that the specs given in this case are at all realistic. I think most contractors would want to add in a consultant's fee and some contingency, if they touched the thing at all. At the very least one would have to spend the money up front on a consultant to determine how crazy the specs are, so you'd have to be kinda "hungry" (or it would have to be a pretty big contract) to deal with it.
And if you're using Romex, you can reduce EMR by twisting it, say about 360 degrees per foot. That way each foot of Romex has an equal amount of hot and neutral on the side you're facing, so current in those two wires are in opposite directions and help to cancel the field. This has been used for over a century in telephone wiring, because interference works both ways. You want to cancel it coming out of the power line, the phone guys want to cancel it getting into their signals.
-- J.S.
Here is a reasonable priced EMF meter. That measure the magnetic field, but not electrical field.
http://www.professionalequipment.com/xq/ASP/ProductID.162/id.6/subID.189/qx/default.htm
That requirement is meaningless unless they specify the protocol that is to be used in making the measurements.
Well if I can hijack my thread back.... :-)
Reading up on code and books (Taunton Press included) that advocate treating code as bare minimum and going beyond it...I don't see how one can live with less than 30-40 circuits in a modern house....dishwasher, clothes washer, dryer, fridge, sump pumps, bathroom heater, etc on separate circuits....external GFCI front and back (and I'd like more in the external garage/workshop)....GFCI for any power tools (OSHA regs anyway for workplaces, why be less careful at home?)....etc etc. ....You'll never have everything running at once but it seems like you need the amperage because you have to wire the house as though it could all run at once...No way that fits in 100A....Let me know if I'm missing anything...
"I don't see how one can live with less than 30-40 circuits in a modern house....dishwasher, clothes washer, dryer, fridge, sump pumps, bathroom heater, etc on separate circuits"
Yes, BUT. So of this is more than the code really requires. They is no need for a separate circuit for each appliance. If they name plate current draw is less than 50% of the circuit rating you can add other applinaces until you get up to 80%.
".external GFCI front and back (and I'd like more in the external garage/workshop)....GFCI for any power tools (OSHA regs anyway for workplaces, why be less careful at home?)....etc etc."
Code requires GFCI for 120 volt outlets in kitchen counter recp, bath recp, and basically any that are in unfinished space (garage or basement) and outdoors.
But here the code is not as strict. You can have an front and back outside receptacle, garage, and basement all on one circuit.
"You'll never have everything running at once but it seems like you need the amperage because you have to wire the house as though it could all run at once...No way that fits in 100A.."
No, the code reconsizes that everything is not running at once. The entrance sizing is determined by 3 watts/sq ft for general lighting and receptacles. plus the 2 20 amp kitchen circuits, plus 20 washer, but for all of the appliances it is based on actual nameplate data, not circuit rating.
Look on the main FHB web page there is a link to an article that gives the worksheet for figuring this.
If your concern is mainly EM fields, I really don't think it is much of an issue but we are all allowed define our own apparent vulnerabilities, you could use a different wiring system.
EMT, Electrical Metallic Tubing or thinwall would be a good alternative to the more common cabling system. Even better, due to the much heavier thickness of the encasing, shielding, conduit wall would be RMC, Rigid Metallic Conduit or heavywall.
Of course installing EMT or RMC, particularly the heavier of the two which requires either expensive threadless connectors or the machining of threads on any cut pieces, is not an inexpensive proposition. Especially in a retrofit or rewire situation where the existing framing and finish surfaces are inthe way and preclude using long length of conduit. This sort of custom and piecemeal installation can multiply the labor costs.
Rewiring a home, with cabling not the more expensive conduit systems, is often twice as expensive as wiring during initial construction when the walls and interior spaces are open.
Actually 4lorn, it is not the thickness of the metal that matters, it is it's conductance and it's resistance to being affected by magnetism.
In military secure communications, where they take electromagnetic interference real seriously, a thin screen of copper is used wherever an aluminum equipment case is not enough. Hi conductance and non magnetic.
If you're gonna use metalic sheathing for EMR in a residence, well grounded EMT is the cost effective way to go.
SamT