lights dim when boiler cycles - can this be helped?

When the boiler in my house cycles, the lights dim all over the house.
Is there anything I can do to limit voltage drops like this? My house has 200amp service; the boiler is on a 20amp circuit with 10 ga aluminum wire (this is the correct size wire for 20amp); and the cable between the socket on the outside of the house and the 200amp panel is enormous.
What can be done? 200amp service for the house is an incredible overkill. My guess is that the house usually draws 40amp or so during busy periods, fewer amps otherwise.
Thanks, Michael
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Time to check all of the connections. Especially the neutrals and grounds. Lights dimming when a motor starts is classic loose neutral.
If your not comfortable working inside the electrical panel hire some one.
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When you say all the connections, do you mean all the connections in the panel or all the connections that are on the boiler circuit (which is a separate circuit)?
I can easily pop open the panel after shutting down the breaker outside the house (the socket has a breaker) and make sure all the grounds and neutrals are tight. If they are tight, then what should I check next?
By the way, the issue is dimming and not flickering. I suspect the latter would be worse although I am not sure.
Thanks,
Michael
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Lights _brightening_ is a sign of loose neutral.
Lights dimming is more of a sign of a loose hot.

Likely a poor connection in one of the main hots. Loose connections don't always show as flickering (flickering is arcing).
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Chris Lewis, Una confibula non set est
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Try moving the boiler circuit to the top of the panel nearest the incoming main power leads. That seems help with AC caused light dimming. Leave the lighting circuit where it is.
Stretch
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snipped-for-privacy@yahoo.com wrote:

Boiler is:
A: Electric B: Gas-fired C: Oil-fired
Is it the "boiler" start-up that dims the lights or is there a circulating pump (Hydronic) which dims the lights when it starts?
The AL wiring raises a red flag in and of itself...
Jim
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Boiler is: A: Electric B: Gas-fired C: Oil-fired
Is it the "boiler" start-up that dims the lights or is there a circulating pump (Hydronic) which dims the lights when it starts?
The AL wiring raises a red flag in and of itself...
Answers:
1. Boiler is oil-fired 2. Boiler start-up dims the lights
Why would AL wire by itself suggest problems? I could pull the wire and replace with 12ga copper but I am not sure what this would do in terms of voltage drops. Would this likely help?
Michael
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snipped-for-privacy@yahoo.com wrote:

Sorry, I didn't mean to imply that the AL wire to the boiler was causing dimming but rather that if the whole house is AL wired there could be connections "somewhere" upstream exhibiting voltage drop under load.
Anyway, some oil burner motors draw significant starting currents today. If the incoming service from the pole is "soft" you'll see dimming (at least on that "phase" or side of the Line). As you note though, a 200 Amp service wouldn't normally be so susceptible.
To really troubleshoot it, you may have to put static loads (a bank of toasters, for example) on the circuit and trace backward with a meter to find where the drop occurs.
Jim
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It's not abnormal. The motor probably draws around 400% of its running current momentarily when it starts. I'm assuming this is an oil burner motor with some circulators as well. Do you know if it is on a dedicated circuit as the more taxed the circuit is when the motor starts, the more noticeable the dimming would be. It is also possible that there is a problem with the motor, which is something the oil burner service folks can check for

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I find it hard to believe a typical burner motor and pump would cause a noticeable flicker on 200 amp panel. There has got to be a wiring problem some where. A typical boiler set up may have a 1/3 HP motor for the boiler and similar or less for the pump. 400% of 1/3 HP motor won't even max out a twenty amp breaker! I have equipment with 5 HP motors running in the shop, feed off of the house's 200 amp panel. There is no noticeable flicker or dimming of the lights when motors start. Greg
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If the lighting circuit happens to be on the same circuit as the burner he should see some dimming when it starts. Not flickering though, that's an altogether different situation. If the burner is on a dedicated circuit and he's getting dimming on a separate lighting circuit, he's probably got a bad connection on that leg of his service or possibly the neutral of the service

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The burner is on a dedicated circuit. I am seeing dimming on a separate lighting circuit.
Does that mean the connection is bad on the lighting circuit or on the burner circuit?
Michael
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Is the dimming only on one lighting circuit or in various locations throughout the house? If it is only on one circuit, I would want to check for an improperly wired "multiwire branch circuit" which is two circuits that share a common neutral. If you can open the panel, identify the affected lighting circuit and the boiler circuit and see if they are connected to a three wire cable, it would indicate this type of connection. Aluminum single strand wire causes a lot of connection problems, however they usually show up as a flickering situation, then go dead altogether

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Ok, I think I may have isolated the problem.
There is a single circuit in the house that dims when a high load turns on anywhere in the house. I managed to cycle the boiler and it caused the lights to dim. I then powered on a table saw and it also caused lights on the suspect circuit to dim.
How do I troubleshoot this circuit?
Should I start in the panel and work backwards?
The circuit has aluminum wires that are spliced to copper with the special purple wire nuts used for AL-CU connections.
Michael
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Yes, I'd check the connection on the circuit breaker and on the neutral buss. However, if it's several reflector floods, like in recessed lights, it doesn't take much of a surge to cause them to dim slightly

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Just another thought that popped into my mind. While you may have a 200 amp service, which is 4/0 aluminum or 2/0 copper conductors on your house, the wire that the utility company uses and the distance you are from the transformer can have a huge impact on voltage drop and dimming. Years ago I worked at a very old house which had a 200 amp service, terrible dimming problems. The wire from the utility company ran for 1000 feet before it reached the transformer and was #6

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The boiler and the circuit that dims are not on a multiwire branch circuit.
Michael
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The breaker box has two buss bars. If most lights and heater are on the same buss, move it to the other side.
Motors draw a lot of current when they start. I can see some of my lights dim slightly when mine starts.
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