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surge protector on mod con?

Wayco Wayne_2
Wayco Wayne_2 Member Posts: 2,472
I just had a customer call with no heat. They had a power line down in their neighborhood and an associated power surge for some reason. they fried a VCR and a television AND the ECM fan motor of their Prestige 175 boiler.  I suggested a whole house surge protector at their breaker panel, but after repairing the boiler and driving home I was wondering if it would be better to put an individual surge protector on the boiler alone. What do you guys think? WW


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I am not a heating professional.

    I did to electrical engineering for a lot of my employment.

    I would suggest a whole-house surge protector to be installed in the Power Panel of the building. It typically keeps surges under 1000 volts. It might be that that is enough to protect the electronics in a mod|con boiler. It depends on the design of those electronics.

    To be safer, though, it would be good to put something like a non-interruptable power supply such as are used with computers just before the input to the boiler. These contain a serious surge protector as well as the battery and stuff. They can protect the boiler down to about 300 volts (depending on the design). Also, some of these UPS units will examine the waveform of the incoming power and if it gets too ugly, will switch to battery power. If you go this route, it is wise to make sure that the unit is big enough to run the boiler for a few minutes, including the circulators, etc. I am not sure how to do this because if my boiler is typical, they are hard-wired into the building (with BX cable in my case), and the surge protectors usually available have plugs and sockets. I am sure an electrician can manage this, but he better know what he is doing.

    And none of this protective stuff will be much help if the power system to the house is not correctly wired. It is best to run a separate breaker to the boiler with nothing else on it. It is vital that all grounding be properly done, and the ground wires as short as possible. Electric codes are meant to protect people, but they do not seem much use against transient voltages, common mode noise, and such.

    But when all is said and done, it is also wise to have insurance because the closer the lightning strikes, the more ineffective any of this protection will be.
  • kcopp
    kcopp Member Posts: 3,823
    Most definately...

    I had a job here is Seacoast Me/ NH and it had issues w/ lockouts..... I went through 2 boards before asking the question about power outages.... "happens 2-3 per day" they said... I went and actually put a UPS (uninterrupted power supply) on the boiler and the problem stopped. I actually recommend them to all my modcon customers... now.

    Think about it we put one on our $1200 PC but not on a $4000 boiler. Does not make sense.

    Glad you are back. kpc
  • Constantin
    Constantin Member Posts: 3,782
    edited March 2010
    I'd love your opinion on the brick wall...

    Specifically, the two outlet model ( To this non-EE who dabbles in electronica, the elimination of MOVs seems like a great idea. I had one installed in ME, to protect a APC UPS, which in turn feeds a Vitodens with electrical juice.

    Most anything electronic in that house has been zapped, damaged, etc. by the many spikes and sags in the electrical supply, but the Vitodens (and the APC) have been unscathed...
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Brick Wall...

    Brick Wall surge protectors work differently from the MOV models.

    Elimination of MOVs would be a great idea because they are sacrificial elements. Each surge suppressed wears them out a little. My whole-house one is made of MOVs and has a green LED that is lit up all the time. If that light goes out, the surge protector is no longer protecting. Who needs that nonsense?

    The question is what kinds of surges do you wish to protect against. The MOV models protect against surges coming in on the hot and on the neutral wires by diverting the surges into the green wire. There are good reasons to do that, and good reasons not to do it.

    The Brick Wall surge protectors protect only from surges coming in on the hot wire, but not on the neutral wire, and they divert the surges onto the neutral wire.

    It is really very tricky to decide which to use, because it depends on exactly what you are trying to protect against. If you are worried about a surge on the hot wire caused by heavy loads being switched on and off on the hot wire, a Brick Wall might be the way to go. On the other hand, if you are worrying about lightning striking nearby, inducing large currents in both the hot and neutral wires, the MOV approach may be better.

    And neither will work very well unless the grounding is not very carefully done, and even that is not always possible because of the way the electrical codes require power panels to be wired. I know the ground wires from my power panel to grounds, while they meet the code, are too long for surge protection, and since they are required by the code to be far apart, they are not ideal for protection against nearby lightning activity. (Nothing will work for direct hits except an adequate insurance policy.) My electricians have been casual about what they connect to the neutral bus bar and to the ground bus bar, claiming (correctly) that they are connected together. That is all very well at 60 cycles, but it is a disaster when high frequency transients are involved. Since I am not a licensed electrician, I have not rewired the grounds and neutrals of my power panel, but I am sorely tempted to do so. OTOH, I think I would be in trouble were I to move the outdoor ground stakes closer to the cold water pipe where the other ground is connected. It is really quite complicated and really requires a qualified engineer to study each installation, and that could cost as much as a boiler. I imagine this is rarely done except in scientific or medical laboratories.
This discussion has been closed.