What is a safety tray and termination device and why have we quoted it ?

It seems like you’re concerned about proper installation and safety standards for hot water tanks in Australia.
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It’s essential to follow the Australian Standards to ensure the safe and reliable operation of these systems and to prevent potential damage and costly repairs..
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Installing a steel safety drip tray under hot water tanks in indoor locations without a floor drain is indeed a requirement outlined by the Australian Standards. .
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This tray serves as a safeguard to catch any leaks from the tank or connections. To make the safety system effective, it’s necessary to have either a 25mm drain or an approved automatic shut-off valve in place. The Mildred Automatic Shut Off Valve, which you recommend, is an example of such a safety device. The valve functions by instantly stopping the water flow if it detects a leak, thereby preventing any potential damage and the need for expensive repairs. 

The fact that it operates on either 4 x AAA or AA batteries, which need to be replaced yearly, makes it a relatively low-maintenance safety device. The audible alarm alerts when the batteries require replacement adds an additional layer of assurance..
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In situations where other plumbers aren’t quoting the same safety measures, it could indeed be a matter of concern. It’s essential to ensure that any professional hired for such installations complies with the relevant safety standards and best practices to protect both your property and your daily use of hot water.