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Today, I was in a hospital. Someone told me that there is a fault in a large washing machine. This fault caused all the CB's in the panel to trip.

The panel has many circuit breakers of different capacities/rated current (10A, 16A, 20A, 25A, and 32A). There is also main CB about 80A as much as I recall.

I checked the panel by myself and all CB were closed. It was just a small issue and he just thought that they are all open. Now, I wonder why did he think of this. Can something like that happen?

What I think is that only the CB of the washing machine will trip in case of a fault. If it did not trip, only the main CB (80A) will trip. Am I right? Are there any situations in which all the circuit breakers trip as a response to that single fault?

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    \$\begingroup\$ Seems very unlikely to me. \$\endgroup\$
    – Norm
    Commented Apr 11, 2018 at 17:03
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    \$\begingroup\$ Seems very unlikely to me too, but depending on the total load on the panel, the washing machine fault could have caused the main breaker to trip, which would remove power to all circuits (but not trip the individual breakers). \$\endgroup\$
    – Peter Bennett
    Commented Apr 11, 2018 at 17:17
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    \$\begingroup\$ I have very rarely seen two breakers trip from a single fault but only when the two breakers had similar ratings. However this is very unusual as normally one will trip first removing the overload from the other. I may of seen two breakers trip from a single fault twice in the last 40 years to put this in perspective. I do overload testing on a daily basis so I see several breakers trip every day. \$\endgroup\$
    – Warren Hill
    Commented Apr 11, 2018 at 19:53
  • \$\begingroup\$ Thank you so much @WarrenHill . You have a great experience :) Thanks everybody for your comments. \$\endgroup\$
    – Michael George
    Commented Apr 12, 2018 at 17:52

2 Answers 2

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Odds are that the tripped CB tripped the main CB, which he interpreted as all were tripped.

This can happen when the fault current is large enough or the Protection Discrimination is not matched up to the loads. Selectivity is the ability to isolate a fault with minimum impact on the system.

Protection Discrimination

Devices close to the load have the lowest current rating and shortest operating time. Devices close to the main panel (or the generator, in this case) have the highest current rating and longest operating time.

If a fault occurs, Fuse A should open. If the current is large enough or A fails to interrupt it, Circuit Breaker B will trip. If A & B fail to interrupt the current, CB C will open. Etc.

Breakers typically have thermal (seconds) and magnetic trip (\$ \alpha \$ to \$ I_{Short\ Circuit} \$). So depending on the side of the fault current, fuse A and some or all of breakers could trip to the main panel.

This is your situation. A current large enough to magnetically trip the washing machine breaker AND the panel breaker, which your co-worker extrapolated as tripping all breakers.

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    \$\begingroup\$ And if the panel breakers are really RCDs of the sort that trip on loss of supply, then blowing the panel supply breaker will trip everything..... \$\endgroup\$
    – Dan Mills
    Commented Apr 11, 2018 at 20:30
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I checked the panel by myself and all CB were closed. It was just a small issue and he just thought that they are all open.

I'm trying to interpret this - does he think CBs that are open (tripped) are actually closed (operational)? Does he not know which direction is which?

I'm basing the following on my experiences with standard CBs in the US both residential and commercial buildings...

CBs often appear closed (operational) when they are in fact tripped - the handle barely moves. One needs to cycle the CB to OFF then back to ON to get them to reset. Is it possible he saw the tripped CB (from the washer) and thought that all the other CBs were also tripped because they looked similar?

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    \$\begingroup\$ He doesn't know which direction is which. He thought that the CB of the machine is open (tripped) because it doesn't work. He thought all CB tripped too because they have the same direction. \$\endgroup\$
    – Michael George
    Commented Apr 11, 2018 at 18:49

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