When I worked at Electrolux prototype and tests machines had to run a minimum of 500 hours constantly, that was what we wanted them to run most managed 650 to 700 and some double that. 

a vacuum motor is at its hotest after you have switched it off because there is no air running through it to cool itoff, Its called heat soak and it is the same with cars too.

As long as the bag is not over full and the filters are clean it can do no harm to run the machine for any lenth of time. 

Hope that helps 

Gareth 

One machine we tested a very quiet one the motor got 15deg hotter in the first 5 minutes after shutdown. It depends on weather there is a lot of sound deadening material in the machine aswell 

William 

To answer your question yes its due to the new improved brush less motor, this motor is similar to the moor found in industrial equipment and they are designed to run 24 hours no problem. I have never seen the new rainbow motor but normal motors like this use a capacitor to start the motor and then its just up to the magnetic fieds inside the motor to carry on the momentum. They spin at much lower speeds normally only 1000 to 3000 rpm were as a normal new vacuum motor like those found in eurekas and bissels will run any were between 27000 - 45000 rpm that's also why they do not last. 

Wap use to have special motors for there standard industial vacuums that were long life brushless motors for machines hooked up to cnc and other industrial equipment.

You could run a normal brush drive motor all day with out it overheating however you would simply run the motor life out in about a month. if you needed a vacuum to last longer than that you would use brush less drive induction motor 

WOW this got nasty fast 

Just to put down how much of a valid thread this is.

My DAD has a carpet cleaning company. he mainly uses two prochem truckmounts but also has a few prtables. 

These units are equipped with auto fill and dump , meaning that when the machine reaches its max capacity it will pump the water out and the machine will als refill itself, with clean water, so you can run them all day wihout stopping.

They are equipped with a 240v dc  fresh water pump fitted with a voltage rectifier converting the power from ac to dc for spraying the cleaning solution.

Recently he had been doing a big job cleaning seats in the theatres, he was basically burning out a pump a day and at nearly      $ 300.00 dollers for these pumps it was getting expensive, It was only when I started talking to the local importer for these commercial pumps that he told me they should never run more than 4 hours at a time or they will overheat and burn out.

These pumps are fitted to a very well known ( in the industry ) professionally carpet extractor by the manufacturer a USA company . Not just that but they fitted them to a machine designed to run for hours at a time.

So Jmurry your question at least in my veiw was a very valid one

Gareth  

Ok as some of you know I own a vac shop and we repair allot of vacuums a day , any were between 20 to 30 machines a day. So I tend to know a thing or two about vacuum reliability. We repair both commercial and domestic machines all makes  

Thermal cutout, in our experience they hardly work, 99% of the motors we replace that are burnt out have thermal cutout.

Dirty air motors WILL in general last longer than a clean air motor for a simple reason, they run at slower speeds and therefore are do not face the same stresses that high speed clean air motor would face 

They have there own cooling fan not relying on the suction air to cool them down so when the machine is blocked or the bag is over full it does not affect the cooling of the motor as it does on a clean air motor. 

Gareth 

Ok then I will add this , My Dad and i co own a cleaning company, we employ 80 cleaning staff and have over a 100+ vacuums in inventory, We clean hotels, offices factory's 

sebo  x1 ( x1 about 2 years  and far to expensive to repair ) these are in the storeroom 

370 also not reliable when fitted with the dommel motor they rarely last 1.5 years withou total meltdown taking out most of the body with them ) fit the older lamb motors from the older 360 you loose some suction but the machine can then do 3-4 years 

Old 360 the best sebo often lasting 8 years 

New bs ok about 3 years 

Karcher uprights, 2 years 

Ivacs up350 about 20( fair last about as long as a new sebo bs about 3 years ,

Numatics of various shape and form  old ones good I have one that is 20 years pld and still going new ones average 2-3 years )

wetrocks bantum 6 & 9 ( uses lamb motors but they two burn out 2-3 years) 

Hoover guardsman Dirty air, never had to replace a motor, I bought these when I first started 10 years ago before they pulled out of SA

Clarkes all there are 20 years old dirty air never given any trouble.

We have more but this is MY PERSONAL OWNERSHIP EXPERIENCE. As the co owner of the company I tend to keep an eye on how long the machines last 

My only regret is I cannot get my hands on any more guardsman machines , I buy every one i can find second hand, funny thing they never need motors just a belt and away you go.

We also have big scrubbers those are fun to play with  

I have one taski swingo ride on , its nice to use, we also have a tennant t20 that runs on lpg, that thing is great but cost more than a BMW 540i new. 

I don't use the felix in the business Its in the shop as a show model, ametek motor does well, what I don't like is how the machine smells after a few uses, I used it at home for a bit, we have pets and it got that Miele smell to it. 

I forgot to add to that list the 5 g 1 sebo's we have, those are nice but they are only a few months old now.

I did import two from the USA and fitted new 220v motors but its two expensive. I really wish we got sanitairs here again. I have used one and they are great. You cannot find them second-hand here.

the problem is that in most vacuums by the time that over load has kicked in the damage is done. Most of them kick in when the motor has already blown to prevent total melt down and heavy lawsuits