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I bought a 120 volts Leviton 5100-PS Surge Protector Strip. I'd like to know if all surge protector strips contain thermal disconnector inside already (like Belkin, APC, Eaton, Leviton)?

What would happen if you plug one of those 120 volt unit into 240 volts ac outlet (say accidentally of course).. would the thermal disconnector activates preventing the burn up of the MOV element or would the MOV and plastic casing catch fire. What do you think?

And how does the behavior compares to when the MOV suffers maximum surge of its surge current rating.. would it also catch fire?

Harper - Reinstate Monica
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Samzun
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    I'd hope that any 240v AC outlet would have the proper receptacle to avoid such an unfortunate event. At any rate, this topic seems outside the scope of home improvement as this site defines it. – isherwood Oct 16 '18 at 13:14
  • But isn't the purpose of thermal disconnector to avoid any fire by disconnecting the MOV from the current path? Or do you mean the MOV is already burning even after the thermal disconnector engages? What is usually the case. – Samzun Oct 16 '18 at 13:46
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    I'm voting to close this question as off-topic because it's an electronics question – mmathis Oct 16 '18 at 14:05
  • pls move it to the electronics thread then because I need to know the behavior of MOV in doubling of voltage as it reacts with the thermal disconnector.. isn't a thermal disconnector supposed to disconnect it... – Samzun Oct 16 '18 at 14:31
  • Vote to close. This looks like someones homework assignment. – Retired Master Electrician Oct 16 '18 at 15:50
  • there's an MCOV of 150v, so you would destroy it instantly (and safely) in a 220v situation. – dandavis Oct 16 '18 at 16:26
  • The unit is made of plastic. Plastic can burn especially when continuous heat is applied. Get a steel bodied one. – Harper - Reinstate Monica Oct 16 '18 at 21:14

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If there is not a thermal disconnect (many do not have) the MOV can catch fire, the way MOV's work is once a spike is of sufficient voltage it will break down and dump the excess voltage to ground or neutral depending on how it's wired. If the spike is large enough or having a long time duration the MOV over heats and usually blows itself apart. The case of the device usually contains the electrical fire as required by UL to be listed. Higher end units do have thermal protection but when these devices open the circuit the protection is usually gone. MOV's can take thousands of hits but go beyond there ability to dissipate the heat and they need to be replaced. This is why most whole house protection units have lights to show if the unit is still functional. Some of the larger models have replaceable blocks that are Basicly large MOV's with a temp sensor that opens once the heat exceeds the mfg rating (think of a thermal fuse like on a dryer or coffee maker)

Ed Beal
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  • My country ac system is 220v. I can't use a 320vac MCOV surge protector because the clamping voltage (or let thru voltage) would be high. Therefore I used a 150vac MCOV SPD connected to a 220v-110v autotransformer. Now I'm concerned that if the autotransformer primary shorted, the secondary can be exposed to the full voltage of the primary. This is why I'm asking if the 150vac MOV can catch fire. Haven't you heard of anyone else using this configuration or combination of 150vac SPD and 220v-110v step-down transformer? This can lower the clamping voltage, isn't it? – Samzun Oct 16 '18 at 20:12
  • Ed. You mentioned that "the way MOV's work is once a spike is of sufficient voltage it will break down and dump the excess voltage to ground or neutral depending on how it's wired". Well.. what would happen if it's line to line (split phase like 120v per phase in the US power system). Where would the excess voltage be dump when you put a 320Vac MCOV across the two 120v phase producing 240 volts? – Samzun Oct 17 '18 at 07:40
  • With split phase the maximum voltage to ground or neutral is 120v RMS , the voltage from each leg is still dumped to ground/ neutral in the main panel the 2 are at the same potential since they are bonded at this location. With 220 v to ground you would normally use a surge protector with a higher breakdown threshold , a step down transformer would work. whole house supressors I normally install need a 30 amp circuit breaker so the transformer would need to be sized around 3.6kva (30*120) since these spikes are short a slightly smaller transformer might hold to use your suppressor. – Ed Beal Oct 17 '18 at 13:19
  • I was asking what is the behavior when you directly connect a MOV between the 2 phases? usually a MOV is connected line to neutral.. or line to ground. but a MOV directly connected between 2 phases without passing thru ground or neutral.. what would happen in this case? – Samzun Oct 17 '18 at 13:23
  • Connecting line to line would not eliminate the spike so you would not hook it up that way. But if it was it would smoke in a matter of seconds as the peak value of the voltage would be above the 320v threshold leg to leg. – Ed Beal Oct 17 '18 at 13:42
  • since each line is 120 volts.. connecting line to line is 240 volts.. so if you put a 320Vac across it line to line.. it won't smoke because 240 volts is the line to line voltage.. about eliminating the spike.. isn't it that it should still do it.. I read that "A Normal mode (L-L) surge will be suppressed by the MOV acting like a rather poor wire but shorting the lines together enough to load down the voltage surge due to the impedance of the wires; which is its normal usage.".. what do you think? – Samzun Oct 17 '18 at 13:59
  • You are thinking in terms of RMS this is the average voltage not the peak to peak value. You need to devide the meter reading voltage by .707 or multiply by 1.414 to get the peak value! Going line to line your spike will be many times the value and not be effective at dampening or suppressing the spike. Please look up Root Means Square (RMS) voltage and the peak to peak values and you will see that 240v RMS has a peak voltage of 339.v in other words every cycle 50 or 60 times a second the MOV will conduct as I said the magic smoke will probably escape, where there is smoke there is fire. – Ed Beal Oct 17 '18 at 14:25
  • Note that MCOV rating (320V) is in rms too and not peak to peak so it wont smoke when you put a MOV across line to line totaling 240V (US power system which i also have). Also directly putting an MOV line to line is one of the basic protection mode of SPDs so i wonder why you think it wont work. Pls elaborate. – Samzun Oct 17 '18 at 19:10