# Can I safely use a 6 A, 600 V diode in place of a 6 A, 400 V diode?

Inexperienced electrical person here, but trying to save significant cost to repair an oven. The oven I have has a MR754 diode off the main convection heating element, that has failed. Unfortunately, since it is part of the wiring, the manufacturer only offers up the entire wiring harness as a replacement part at $500+. Pending all other things checking out with a multimeter, I would like to simply splice in a replacement diode (~$2 part). However I cannot locate an MR754 in my area and it's multiple business days to get one delivered via online order. Local vendors do have an MR756 available. Both are 6 amp current, but the available replacement would be 600 V vs 400 V. Is this safe to use in this application? What is the risk, should I try this? Do I put the other components in the oven (i.e. element or control board) at risk?

• I see no reason why not. 600 V is only the reverse block rating. – skvery Apr 3 at 6:18
• I think it would even be safer. More tolerance if anything goes wrong. – PNDA Apr 3 at 10:55
• I there is a VTC-repair against this question, but I don't think it's applicable. This is a very specific question about one type of component, that can be easily answered. A "repair question" is for "my widget broke, here's a blurry photo of half the circuit board, where should I put my \$4 multimeter?" – pipe Apr 4 at 10:34

Yes, higher voltage rating is fine. It just means more safety margin against mains transients (which is good). The only difference between the -4 and the -6 is the voltage rating (see datasheet).

• The diode in itself is certainly fine, as you say very adequatly - but the question also asks if there are any other risk factors in changing it. You seem to have a good grasp (judging by tenure and rep) - are there none worth mentioning? – Stian Yttervik Apr 3 at 11:01
• A larger diode could have large leakage currents but that usually isn't a concern on mains stuff. – ACD Apr 3 at 12:48
• @StianYttervik there may be risks for OP that would exist working on any mains powered appliance. You could write an answer highlighting those and I will upvote it if it is useful. I don’t see any special risks here in replacing one part with another OEM equivalent. – Spehro Pefhany Apr 3 at 12:51
• @ACD higher rated voltage is usually the exact same die. Bigger diodes are those rated for more current, not voltage. If anything a higher rated diode of the same type would likely have less leakage. – Spehro Pefhany Apr 3 at 12:52

Generally as the comments and answers already state it's ok to use a diode of higher voltage rating when the amp rating is sufficient. It would even be ok to have a slightly higher amp rating normally.

In your case however i see no fuse in the wiring diagram and it looks like the diode could have blown due to a defective heating element.

A short circuit within the heating coil will cause the current to go up and this will as a result destroy the diode when it's going over 4 amps. Since it is more likely for a heater coil to wear off and fail than the diode you should check the heating element first. You might see your replacement diode fail very soon otherwise.

• Yes, thank you. I did check resistance across the element itself and it holds steady in the mid-40's. Seems that it checks out? – LTB Apr 3 at 15:30
• @LTB I don't see right now what voltage the oven runs at, but 40Ohm is probably too little - on the other hand you are measuring cold and I assume the heating element's resistance grows with temperature (but you could still have peak currents higher than 6A, depending on voltage). – Nobody Apr 3 at 17:04
• @LTB: 40 Ohm sounds reasonable for a 120V country; I measured the stovetop elements in my stove (Canada: 120V) out of curiosity when replacing a damaged one (ceramic coating chipped), and IIRC the smaller ones were like 50 ohms. 120^2 / 40 is 360W for 120Vrms across it, which sounds totally reasonable for an element. And 120V / 40 ohm is 3 amps RMS, so peak still comfortably less than the 6A rating. – Peter Cordes Apr 3 at 18:22
• @Nobody: the OP is probably in a 120V country; 3A RMS would nicely explain a 6A diode rating. See my previous comment. I'd guess North America judging by the 3 languages in the manual: English, Spanish (I think), French. – Peter Cordes Apr 3 at 18:26