Surge Protection for High Efficiency Condensation Boiler??

do we need special surge protection

I am a homeowner with a clever electronics board in his mod-con boiler with outdoor reset; I am not a heating professional, nor do I play one on TV. I did do a lot of electrical engineering up until about 1965, but my current knowledge of this is probably pretty out of date.



Some of the electronics in these systems do need surge protection. The big question you will need to answer is what kind of surges do you intend to protect against. Because the only protection against a direct lightning strike is a suitable paid up insurance policy. As far as surges and dips are concerned, dips will probably cause little problem, although they can burn out some motors. Such as in your boiler, refrigerator, A/C, and such. Not your old analog clock if you still have one. The motors in circulators such as the Taco 00 series should have no problems with inadequate input voltage (though they might not pump hard enough).



The biggest thing to worry about is voltage spikes. These can be caused by a tree branch falling on your power lines, or ice forming and a sufficient wind to cause wires to touch. If you are unlucky, you might get this when a large motor in your house shuts off. Lots of other things can cause spikes, and you have little control over them. In other words, not all threats come from outside your house, and they are not all caused by lightning.



1.) Most of the sensors on my system (temperature measurements) are just variable resistances of about 10K ohms at some temperature or other. The hotter they get, the lower the resistance. The other sensors are just contacts, such as the aquastat in my indirect fired domestic hot water heater. My two thermostats are little Honeywell boxes that are powered by three AA cells. If lightning strikes close enough, it might take out the thermostats, but that is about it.



2.) Surges -- a temporary increase in line voltage that last long enough to detect with an ordinary AC voltmeter -- do not normally cause problems if they do not go too high or last too long. The power supply in your boiler control should be designed to take care of this (I do not know if they are). They can also deal with sags if they are not too deep, but I do not know if they do. My boiler is just starting its fourth heating season and I have not experienced any trouble with this.



3.) Spikes -- momentary increases of line voltages, sometimes very short (0.1 microsecond or less, but they can be longer too) -- are probably the most likely to harm electronic equipment. You will never see these on AC voltmeters, but a sufficiently fast oscilloscope can find many of them. Power supplies can be designed to guard against most of these, but I do not know if the ones in home heating boilers are designed for this.



There are two things you can do about spikes. One is to install a whole-house surge protector in your main power service panel. These clip the spikes down to about 1000 volts or less. Unfortunately, they do not go much lower, like 200 volts or something. There are good engineering reasons why they cannot, but that does mean they do not protect against everything.



The other thing you can do is install a suitable Uninterruptable Power Supply to supply your boiler, and locate it as close to your boiler as possible. The UPSs normally come with a pretty good surge protector in it. If you use both a whole house surge protector and a UPS, you are probably as well protected as you can be. The advantage of the UPS is that it can protect against some smaller spikes, and it can also run your boiler for a while if you get a big enough one.



I have a whole house surge protector in my service entry panel. One of these (page 11):



http://static.schneider-electric.us/docs/Electrical%20Distribution/Surge%20Protective%20Devices/Residential%20Whole%20House/6671CT9701.pdf



The one to get, though, is one designed for the service panel you actually have. Mine is a particular series Square D panel. While it is easy enough to put one of these in your power panel, I got a professional licensed electrician to do it so as not to annoy my insurance company. The labor was more than the cost of the surge protector. But parts and labor were less than a new control board would cost; about half the price of the board.



I have not added a UPS because I would want it to power the circulators as well for long enough for the power company to repair their power lines, and a unit that big is too expensive. The longest interruptions around here are in the summer when the boiler makes only domestic hot water, and I can wait for that.



The only problem I had with the control board in my W-M Ultra 3 was when the control board got under water. It started giving out all kinds of bizarre error messages and the boiler did not run right. My techie dried off the whole thing and we tried it and it still worked. The factory rep gave us a new board because he did not want me running with a board that had been under water. Probably wise, but it shows how tough that board is. We did figure out where the water came from and fixed that before we put in the new board. Locating the water leak took almost a week. It was very slow and happened only when the boiler was firing.