Fuso briefing explores EV safety

Truck Efficiency
Fuso, part of Daimler Trucks, tackled high voltage safety in some detail during its extended press briefing for the new eCanter, recently held in Portugal. Lucy Radley was there

All electric vehicles must conform to UNECE-R100 in order to obtain type approval, but it turns out that this global regulation, aimed at protecting drivers and passengers in EVs first and foremost, is just the tip of the iceberg. In a workshop presented by Marc Ehlers, CESC for Fuso Europe, the main message was all about the appropriate training being made available for all who may need it.

Internally, there is one basic rule in place across all Daimler electric trucks and buses when it comes to high voltage safety (and this includes the Fuso brand that it markets in Europe). This dictates that no one may work on these vehicles without first undertaking the relevant Daimler-provided qualification. Further to that, anyone coming into contact with a high voltage (HV) vehicle on a regular basis must also be qualified as dictated by Daimler’s HV safety organisation pyramid (see diagram) – right down to the person who comes in to wash the trucks down at weekends.

At the top of this hierarchical structure, and compulsory in all Daimler workshops handling BEVs, is a chief electrics specialist in charge, or CESC. This is someone who has undertaken a higher level of training to fulfil the role: often a workshop manager, but the option is there to appoint a nominated person from elsewhere in the team. Either way, the CESC is responsible for making sure that no one unqualified goes near any high voltage vehicle to work on it. Different levels of training are available to suit the task being undertaken; our truck washers, for example, would only need a vehicle introduction, to locate external features such as charging sockets.

It is also important to note that the qualifications Daimler provides are specific to each model. Regular refresher training on each type is also a must, especially if contact with one model is infrequent.


If this all sounds a little onerous, it’s not without precedent. “The logic comes from German law, but we mandate that all our workshops in all our markets across the world – including Japan – should use it,” Ehlers tells us. “It is also written clearly into all manuals for the product that strictly only qualified persons for eCanter are able to work on it.”

On paper this is all well and good, but what will happen if each OEM adopts a methodology based on their own home country’s legal framework, especially in multi-brand dealerships? Perhaps more importantly for us, when the UK sets its own standard, which will take priority? The answer to the second question is, we’re told, that the German way of doing things is usually more strict than other countries, therefore all will be well.

When it comes to multi-brand dealerships and independents, however, an awful lot of this will have to be a matter of trust – sure, OEMs can stipulate methods stricter than geographically required for vehicles under warranty, but with no legal compulsion to continue that method beyond that period, only time will tell how this will play out in the longer term. Ehlers himself, incidentally, is fairly pragmatic. “In Germany we are very conservative and safe, which from my point of view is the correct approach at the moment,” he says. “Maybe in six or seven years we will be saying something different, because by then everyone will be more familiar with high voltages, but not for now.”

Moving on to the vehicle itself, Ehlers shows us the ropes on a chassis cab with the cab tilted so the entire HV system is visible. The basic rule is not to touch orange cables, as they are the ones which may present some kind of danger. This vehicle has been fully decommissioned, so there is no high voltage present at all.

Decommissioning an electric vehicle basically involves isolating both the high voltage and low voltage battery. The latter is present to run auxiliaries, but also to start the high voltage system, so simply turning the ignition off and removing the key is not sufficient. Again, under German law it is also necessary to check there really is no voltage in the system, so a breakout box between various components is used – as long as the voltmeter reads less than 20V, all is considered to be well.

Having established this, Ehlers is able to demonstrate how, in reality, merely touching a high voltage orange cable will have little effect. If one were to be cut, immediately under the orange outer cover is a layer of rubber hose. This only provides mechanical protection. It is the layer of metal mesh beneath – known as armouring– which offers shielding from electromagnetic fields. Beneath that is a second rubber hose before finally the copper wire itself is reached. In other words, to damage a cable badly enough to come in contact with live current would require quite some effort.

Should you get that far, however, at some point there would inevitably be contact between the metal shielding and the copper. This signals to the high voltage system that there is an isolation failure, whereupon it will shut off. Continuous monitoring is achieved by measuring the resistance in the system on both positive and negative sides. “Normally it is about 2.5MΩ, so very high resistance,” Ehlers tells us. “If it becomes lower than 200kΩ, a warning light will appear on the vehicle and it will not start.”

All this aside, it is very unlikely that a high voltage shock could be received from eCanter, simply because the vehicle itself is electrically isolated. “If I could touch a positive wire, I cannot close the circuit because the vehicle is not grounded,” Ehlers assures us. Touch both ends of a cut wire and a short, sharp shock would be delivered, but this would not be enough to cause significant injury: equipotential bonding, as seen attached to metal pipework in houses, connects the housing of each high voltage component to the chassis frame. Electricity always takes the path of least resistance, so if there is a short circuit, it will travel between components. This, too, will lower resistance in the battery, signalling the HV system to shut off.

Yet still there’s more. Each high voltage connector is fitted with a bracket to ensure it can’t be removed without a specific tool, meaning that removal would have to be planned. Inside these connectors is an interlock circuit breaker, to prevent arcing or sparking. There is a pyro fuse controlled by the battery ECU which will fire in case of a hard impact or roll-over, disconnecting the global power supply. Then, finally, the last layer of defence is a good old-fashioned emergency stop button.

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