AC can use a ratio transformer for 150/5A however for DC this is not so. With an 150A ammeter having an internal shunt at a measured 78.1mohm a secondary shunt is used at a 2.7mohm, when you do the math it doesnt quite add up 30:1 ratio so real world testing needs to be done but you get the idea. Changing the load resistor or voltage wont impact the set ratio of both shunts.
